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WO2015144572A1 - Têtes de capteur électrochimique à base de diamant - Google Patents

Têtes de capteur électrochimique à base de diamant Download PDF

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Publication number
WO2015144572A1
WO2015144572A1 PCT/EP2015/055874 EP2015055874W WO2015144572A1 WO 2015144572 A1 WO2015144572 A1 WO 2015144572A1 EP 2015055874 W EP2015055874 W EP 2015055874W WO 2015144572 A1 WO2015144572 A1 WO 2015144572A1
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Prior art keywords
diamond
boron doped
electrically insulating
micrometres
electrodes
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Inventor
Maxim JOSEPH
Eleni Bitziou
Nicola Louise PALMER
Timothy MOLLART
Mark Edward NEWTON
Julie Victoria Macpherson
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Element Six Technologies Ltd
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Element Six Technologies Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/28—Electrolytic cell components
    • G01N27/30—Electrodes, e.g. test electrodes; Half-cells
    • G01N27/308—Electrodes, e.g. test electrodes; Half-cells at least partially made of carbon

Definitions

  • Certain embodiments of the present invention relate to diamond based electrochemical sensor heads and methods of fabricating the same.
  • Diamond can be doped with boron to form semi- conductive or fully metallic conductive material for use as an electrode. Diamond is also hard, inert, and has a very wide potential window making it a very desirable material for use as a sensing electrode for an electrochemical cell, particularly in harsh chemical, physical, and/or thermal environments which would degrade standard metal based electrochemical sensors.
  • the surface of a boron doped diamond electrode may be functionalized to sense certain species in a solution adjacent the electrode.
  • diamond material is inherently difficult to manufacture and form into suitable geometries for sophisticated electrochemical analysis.
  • diamond electrodes utilized as sensing electrodes in an electrochemical cell have tended to be reasonably simple in construction and mostly comprise the use of a single piece of boron doped diamond configured to sense one physical parameter or chemical species at any one time. More complex arrangements have involved introducing one or more channels into a piece of boron doped diamond through which a solution can flow for performing electrochemical analysis.
  • the present applicant is unaware of sophisticated diamond based electrochemical sensors which can perform multiple sensing functions at the same time, particularly configured for use in harsh environments. Due to the inherent difficulties involved in manufacturing and forming diamond into multi- structural components, even apparently relatively simple target structures can represent a significant technical challenge.
  • WO2005/012894 describes a microelectrode comprising a diamond layer formed from electrically non-conducting diamond and containing one or more pin-like projections of electrically conducting diamond extending at least partially through the layer of nonconducting diamond and presenting areas of electrically conducting diamond at a front sensing surface.
  • a number of different fabrication routes are disclosed for obtaining such structures. One route is described as follows. An insulating diamond layer (natural or synthetic) may be polished flat and parallel.
  • This layer may then have features etched into one face, using for example plasma or chemical etching through a mask, chemical etching of implant damaged features, or laser etching, to generate etch features which when filled will become the electrodes.
  • a boron doped diamond layer may then be grown by CVD methods onto this patterned surface, such that it fills the recesses processed into the surface. Polishing from the front removes the continuous boron doped layer and reveals a planar sensing surface with isolated regions of boron doped diamond material surrounded by an electrically insulating diamond support matrix. Further processing from the rear face can provide either a continuous contact layer or individual connections. For example, one approach involves laser drilling to a rear surface of the boron doped regions followed by filling with metallisation and individual wire bonding.
  • WO2005/012894 also discloses that an interconnection layer or layers on the back of the layer presenting the analysis surface may also be boron doped diamond or as an alternative may be graphite, which may be grown or implanted, or generated in situ by laser or implantation damage, possibly modified by subsequent annealing.
  • Other alternatives include metals which may be deposited and patterned using any standard technique such as vapour deposition, sputter deposition, electroplating, laser ablation etc.
  • WO2012/126802 describes a similar diamond based electrochemical band sensor comprising a plurality of boron doped diamond band electrodes disposed within a diamond body. Each boron doped diamond electrode has a length / width ratio of at least 10 at a front sensing surface of the sensor. It is described that it is advantageous from a functional perspective for certain sensing applications to provide band electrodes which have a high aspect ratio at the sensing surface such that a length of a band electrode across the sensing surface is very much larger than a width of the band electrode.
  • WO2013/135783 disclosed optimized boron doped diamond materials for electrochemical sensing applications which have a high boron content and a low sp2 carbon content which can be used to form boron doped diamond electrodes which has a broad solvent window, a high degree of reversibility, and a low capacitance.
  • One problem the present inventors have found with the aforementioned approach is that following the technique of patterning the surface of an electrically insulating diamond substrate to form trenches which are then filled with boron doped diamond material using a CVD overgrowth technique, the geometry of the trenches and the growth parameters used in the CVD overgrowth technique must be carefully controlled to obtain filling of the trenches with boron doped diamond without the formation of voids and also to ensure that such filling can be achieved with high quality boron doped diamond material optimized for electrochemical sensing applications.
  • One way to mitigate the aforementioned problem is to form shallow trenches in the electrically insulating diamond substrate which are easier to fill with boron doped diamond material using a CVD overgrowth technique.
  • this approach is itself problematic for a number of reasons. For example, after overgrowth of boron doped diamond material the deposited boron doped diamond material must be processed back to reveal the boron doped diamond electrode structure.
  • Diamond surface processing techniques are not as accurate as, for example, silicon processing techniques, and if the boron doped diamond electrode structure is very thin then it can be difficult to process back the deposited boron doped diamond material to reveal the electrode structure without processing off the electrode structure or alternatively not consistently revealing the electrode structure without leaving some boron doped diamond material over other portions of the sensing surface.
  • the electrode structure is made very thin then the electrodes have a higher electrical resistance in the plane of the sensing surface leading to a potential drop over each electrode sensing surface and a decrease in the reversibility of the electrodes in electrochemical sensing applications.
  • the electrode structure is made very thin then it can be difficult to cut through the electrically insulating diamond support matrix to a rear surface of a thin boron doped diamond electrode disposed therein to form vias for rear electrical connections without either falling short of the rear surface of the thin boron doped diamond electrode or otherwise over- shooting the rear surface and drilling through to the front sensing surface of the boron doped diamond electrode.
  • a diamond electrochemical sensor head comprising: a planar sensing surface; a rear surface through which electrical connections are provided; one or more boron doped diamond electrodes which are disposed within trenches in an electrically insulating diamond support matrix at the planar sensing surface, the one or more boron doped diamond electrodes extending partially through the electrically insulating diamond support matrix from the planar sensing surface towards the rear surface of the electrically insulating diamond support matrix; one or more vias extending from the rear surface of the electrically insulating diamond support matrix to a rear surface of the one or more boron doped diamond electrodes within the electrically insulating diamond support matrix; one or more ohmic contacts disposed on the rear surface of the one or more boron doped diamond electrodes within the vias in the electrically insulating diamond support matrix; and one or more electrical connectors extending through the one or more vias to the one or more ohmic contacts disposed on the rear surface of the one or more boro
  • a method of fabricating a diamond electrochemical sensor head comprising: starting with an electrically insulating diamond substrate having planar front and rear surfaces and a thickness between said planar front and rear surfaces in a range 50 micrometres to 1.5 millimetres; cutting one or more trenches in the planar front surface of the electrically insulating diamond substrate, wherein the one or more trenches have a depth in a range 20 micrometres to 500 micrometres; growing boron doped diamond material over the front surface of the electrically insulating diamond substrate and into the one or more trenches; processing back the boron doped diamond material over the planar front surface of the electrically insulating diamond substrate to form a planar sensing surface comprising one or more boron doped diamond electrodes surrounded by an electrically insulating diamond support matrix, the planar sensing surface having a surface roughness R a less than 100 nm after processing, the one or more boron doped diamond electrodes
  • the solvent window meets one or both of the following criteria as measured by sweeping a potential of the boron doped synthetic diamond material with respect to a saturated calomel reference electrode in a solution containing only deionised water and 0.1 M KNO 3 as a supporting electrolyte at pH 6: the solvent window extends over a potential range of at least 4.0 V wherein end points of the potential range for the solvent window are defined when anodic and cathodic current density measured at the boron doped synthetic diamond material reaches 38 mA cm "2 ; and the solvent window extends over a potential range of at least 3.0 V wherein end points of the potential range for the solvent window are defined when anodic and cath
  • growth conditions are controlled such that an interface region between the one or more boron doped diamond electrodes and the electrically insulating diamond support matrix comprises no voids having a largest lateral dimension greater than 10 micrometres, 5 micrometres, 1 micrometres, 500 nanometres, 300 nanometres, or 100 nanometres.
  • the one or more ohmic contacts disposed on the rear surface of the one or more boron doped diamond electrodes within the vias in the electrically insulating diamond support matrix are formed of non-diamond carbon, e.g. graphite.
  • One problem with the aforementioned methodology is that it is difficult to form a metal ohmic contact on the rear surface of the boron doped diamond electrodes through narrow laser-cut blind holes or trenches forming vias in the rear of the electrically insulating diamond support matrix. It has been found that the rear surface of the boron doped diamond electrodes can be graphitized using a laser and such a graphitized or non-diamond-carbon surface within the through-hole provides an ohmic contact which is suitable for electrochemical sensor application. Some of the non-diamond-carbon rear contact can be removed by acid cleaning after formation. In this regard, it is advantageous to provide a relatively thin layer of non-diamond carbon for the ohmic contact to present a low resistance contact.
  • the ohmic contact is formed to have a low resistance per unit area of, for example, no more than 10 ⁇ cm "2 .
  • Laser pulsing and cross-hatching can be used to ensure an even cut during laser cutting to form the vias which can ensure that there is no "drill-through" to the front sensing surface and can also aid in providing a relatively uniform, low resistance ohmic contact.
  • Figure 1 shows a schematic flow diagram illustrating a fabrication method for manufacturing a diamond electrochemical sensor head.
  • Figure 2(a) is a further schematic illustrating the step-by-step fabrication of an all-diamond electrode.
  • Figure 2(b) shows 3D schematics of different all-diamond pBDD electrodes fabricated using the process illustrated in Figure 2(a) including: (i) dual band; (ii) triple band; (iii) multiple bands; (iv) disk; (v, vi) ring-disk.
  • Figures 2(c)(i) to 2(c)(iii) show FE-SEM images of all-diamond devices: (i) triple band (in- lens); (ii) macrodisk (secondary electron; SE); and (iii) ring-disk (SE).
  • Figure 2(c)(iv) shows an optical photograph of a top contacted ring-disk (disk is 3 mm diameter).
  • Figure 3 is a further schematic illustrating a step-by-step fabrication for the production of co- planar, individually addressable boron doped diamond (BDD) electrodes insulated in diamond, top and back contacted, at both the micro- and macroelectrode scale.
  • BDD boron doped diamond
  • Figure 4(a) illustrates back contacting of all-diamond electrodes via an in-lens FE-SEM image of a cross-sectioned macroelectrode disk structure.
  • the pBDD is clearly evident as a region of lighter contrast at the top of the image.
  • the internal surface of the electrode is contacted by laser micro machining a hole through the insulating diamond to the pBDD layer.
  • Inset shows a photograph looking through the transparent top surface of a multiple band electrode (at least seven black, boron doped, electrodes are visible).
  • the lasered back contacts are visible as black cones.
  • the bands are each 180 ⁇ wide.
  • Figure 4(b) illustrates back contacting of all-diamond electrodes.
  • White light interferometry cross-sectional depth profiles are shown which were taken at various stages during the laser micromachining process, demonstrating a high level of depth control.
  • the y axis has been normalized with respect to the thickness of the diamond wafer (1 mm).
  • the dotted line indicates the front electrode face of the diamond sensor head.
  • Figure 5(a) shows, for all-diamond, individually addressable, back contacted band electrodes, typical Raman spectra recorded from higher (lower trace) and lower (upper trace) doped grains on an electrode with width of 200 ⁇ .
  • the inset shows a photograph of a ten band electrode device. Band lengths were all 10 mm and of widths in the range 50 ⁇ to 1 mm.
  • Figure 5(b) shows experimental (solid lines) and simulated (dashed lines) cyclic voltamograms for 1 mM Ru(NH 3 ) 6 3+ reduction/oxidation recorded at 100 mV s "1 , in 0.1 M KNO 3 , on different width pBDD band electrodes, 1 mm, 500 ⁇ , 200 ⁇ , 100 ⁇ , and 50 ⁇ .
  • the inset shows solvent windows recorded in 0.1 M KNO 3 at 100 mV s "1 for the same five electrodes.
  • Figure 6 shows a schematic diagram of a 3D band system.
  • the BDD electrode is labelled surface 1.
  • the insulating diamond surface is labelled 2.
  • the external surfaces of the solution that define the volume are labelled 3.
  • a 2D section has been taken through the 3D model.
  • the identity of the faces is shown on the projected face on the right hand side.
  • the radial model for the ring-disk is also shown, where the ring and disc are labelled la and lb, respectively.
  • the inert diamond surface is boundary 2, the closed volume edge boundaries are labelled 3.
  • the ring-disk system has an additional boundary of axial symmetry that is labelled 4.
  • Figure 7 shows experimental (solid lines) and simulated (dashed lines) CVs for 1 mM Ru(NH 3 ) 6 3+ electrolysis in 0.1 M KNO 3 at a BDD ring electrode of dimensions 3.1 mm and 3.2 mm inner and outer diameters respectively at a scan rate of 10, 20, 30, 50, 100, 300, and 500 mV s "1 .
  • Figure 8 shows in-lens FE-SEM images (i) and corresponding AFM images (ii) of the boundary between insulating and pBDD regions across two different pBDD band electrodes
  • Figure 9 shows FE-SEM images of all-diamond electrodes including: (a) an in-lens SEM image of a dual band structure with the inset shows a cross section of the same device; and
  • Figure 10 shows an example of a defected ring-disk electrode system.
  • Figure 10(a) shows an FE-SEM image of a ring-disk system with the defect clearly visible as a dark line along the inner perimeter of the ring electrode. The defect region is expanded in the inset. Both scale bars are 100 ⁇ .
  • Figure 10(b) shows a corresponding solvent window for the ring electrode in 0.1 M KNO 3 at 100 mV s _1 .
  • Figure 11 shows characterisation data for a 1.02 mm diameter all-diamond macro electrode: (a) CV with 1 mM Ru(NH 3 ) 6 3+ ; and (b) solvent window and (inset) Raman data showing no evidence of non-diamond-carbon (NDC).
  • BDD Boron doped diamond
  • BDD for electrochemical applications is typically either as-grown in nano crystalline (nc) thin film form on a conducting or insulating substrate, or polycrystalline (p) and thick enough to be removed from the growth substrate in a freestanding form.
  • NDC Non-diamond-carbon
  • insulating polymer such as PTFE (Rao et al, Anal. Chem. 1999, 71, 2506-11; Salimi et al, The Analyst 2004, 129, 9), epoxy (Prado et al, Analyst 2002, 127, 329-332) or PEEK (Svorc et al, Bioelectrochem. 2012, 88, 36-41) to produce electrode formats more akin to commercially available, conventional electrode materials such as Pt, Au, glassy carbon. Disk electrodes with diameters in the range tens of ⁇ (Wakerley et al, Chem. Comm. 2013, 49, 5657-9) to several mm (Hutton et al, Anal.
  • PTFE Ro et al, Anal. Chem. 1999, 71, 2506-11
  • Salimi et al The Analyst 2004, 129, 9
  • epoxy Prado et al, Analyst 2002, 127, 329-332
  • PEEK Svorc et al, Bioelect
  • pBDD microelectrodes have also been produced by growing thin films of pBDD onto sharpened W wires and sealing with epoxy and glass (Sarada et al, Electrochem. Soc. 1999, 146, 1469-1471).
  • the mechanical and chemical stability of the material used to insulate is always inferior to that of the pBDD, limiting potential applications.
  • ncBDD thin film ncBDD, patterned to isolate insulating diamond overgrowth from defined regions resulted in a non-addressable recessed ncBDD UME electrode array (Hees et al, Chem. 2013, 19, 11287-92).
  • a micro- electrode is one with at least one lateral dimension less than 1 mm.
  • Single or multiple individually addressed electrodes can be produced on one device.
  • the methodology is exemplified by demonstrating the fabrication and characterisation of individually addressable disks, bands, and ring-disk geometries, suitable for a wide range of electrochemical applications. All-diamond devices are fully characterized using Raman spectroscopy, electron microscopy, conductivity measurements, and electrochemistry.
  • Figure 1 shows a schematic flow diagram illustrating a fabrication method for manufacturing a diamond electrochemical sensor head as described below.
  • the fabrication method starts ( Figure 1(a)) with an electrically insulating diamond substrate 2 having planar front and rear surfaces 4, 6 and a thickness t in a range 50 micrometres to 1.5 mm. At least the planar front surface may be processed to have a surface roughness less than 100 nm although this is not considered essential for the starting substrate.
  • the substrate should have a suitable thickness to receive the overgrown electrodes and providing sufficient mechanical robustness while not being overly thick so that it is suitable for forming reliable back contacts to the electrodes through a rear surface of the substrate in a cost effective manner.
  • the thickness from the planar sensing surface in which the one or more boron doped diamond electrodes are disposed to the rear surface of the electrically insulating diamond support matrix may be no less than 75 micrometres, 100 micrometres, 150 micrometres, or 200 micrometres, and/or no more than 1 millimetre, 750 micrometres, 500 micrometres, 300 micrometres, or 200 micrometres, or any combination of these upper and lower values.
  • the planar front surface 4 of the electrically insulating diamond substrate 2 is then patterned by cutting one or more trenches 8 therein (Figure 1(b)).
  • the one or more trenches 8 have a depth d in a range 20 micrometres to 500 micrometres and/or a width-to-depth aspect ratio w/d of at least 1.
  • the minimum depth of the trenches is defined such that boron doped diamond electrodes formed therein can be reliably surface processed at the front sensing surface, reliably back-contacted without forming through-holes to the front sensing surface, and so that the resultant electrodes are not too thin that in-plane resistance is too high and reversibility of the electrodes in use is impaired.
  • the maximum depth of the trenches is defined such that the trenches can be reliably filled with boron doped diamond material via overgrowth without forming voids within the trenches and in particular so that such trench filling can be achieved using suitable CVD diamond growth conditions to simultaneously provide high quality boron doped diamond material having excellent electrochemical characteristics.
  • the depth of the one or more trenches may be no more than 400 micrometres, 300 micrometres, 200 micrometres, or 100 micrometres, and/or no less than 30 micrometres, 40 micrometres, or 50 micrometres, or any combination of these upper and lower values.
  • the cutting of the one or more trenches 8 should be controlled such that the trench walls and base have a root mean squared surface roughness R q no more than 5 micrometres, 4 micrometres, 3 micrometres, 2 micrometres, or 1 micrometre as this aids overgrowth and filling of the one or more trenches without the formation of voids.
  • trench walls in Figure 1(b) are illustrated as being vertically oriented, according to certain embodiments the trench walls may be angled inwards to aid in trench filling during overgrowth (indicated by dotted lines in Figure 1(b)) without the formation of voids.
  • trench walls which are angled outwards to form an overhanging structure should be avoided as this can lead to the formation of voids under such an overhanging structure.
  • Boron doped diamond material 10 is then grown over the front surface of the electrically insulating diamond substrate 2 and into the one or more trenches 8 as illustrated in Figure 1(c).
  • CVD diamond growth parameters can be controlled in such a way as to achieve filling of the one or more trenches 8 without the formation of voids.
  • CVD diamond growth parameters can simultaneously be controlled such that the boron doped diamond material 10 has a high concentration of boron dopant with a low sp2 carbon content to ensure that the boron doped diamond material filling the one or more trenches has the following characteristics: a solvent window meeting one or both of the following criteria as measured by sweeping a potential of the boron doped synthetic diamond material with respect to a saturated calomel reference electrode in a solution containing only deionised water and 0.1 M KNO 3 as a supporting electrolyte at pH 6: the solvent window extends over a potential range of at least 4.0 V wherein end points of the potential range for the solvent window are defined when anodic and cathodic current density measured at the boron doped synthetic diamond material reaches 38 mA cm "2 ; and the solvent window extends over a potential range of at least 3.0 V wherein end points of the potential range for the solvent window are defined when anodic and cathodic current density measured at the
  • a microwave plasma activated CVD diamond synthesis system typically comprises a plasma reactor vessel coupled both to a supply of source gases and to a microwave power source.
  • the plasma reactor vessel is configured to form a resonance cavity supporting a standing microwave, typical frequencies used for this heating application include 2.45 GHz and approximately 900 MHz depending on the RF spectrum allocation of each country.
  • Source gases including a carbon source and molecular hydrogen are fed into the plasma reactor vessel and can be activated by the standing microwave to form a plasma in high field regions.
  • a suitable substrate is provided in close proximity to the plasma, reactive carbon containing radicals can diffuse from the plasma to the substrate and be deposited thereon. Atomic hydrogen can also diffuse from the plasma to the substrate and selectively etch off non-diamond carbon from the substrate such that diamond growth can occur.
  • a source of boron such as diborane gas is introduced into the synthesis atmosphere then boron doped synthetic diamond material can be grown.
  • Single crystal synthetic diamond materials are typically fabricated via homoepitaxial growth on single crystal diamond substrates.
  • polycrystalline synthetic diamond material can be grown on silicon substrates, refractory metal substrates, or on polycrystalline diamond substrates.
  • Important growth parameters include the microwave power density introduced into the plasma chamber (typically ranging from less than or equal to 1 kW to 5 kW or more for a substrate area ⁇ 20 cm 2 ), the pressure within the plasma chamber (typically ranging from less than or equal to 50 Torr (i.e. 6.67 kPa) to 350 Torr (i.e.
  • the gas flow velocity flowing through the plasma chamber typically ranging from a few 10s of seem (standard cm 3 per minute) up to hundreds or even thousands of seem
  • the temperature of the substrate typically ranging from 600 to 1200°C
  • the composition of the synthesis atmosphere typically comprising 0.5 to 20% by volume of carbon containing gas (usually methane) with the remainder of the synthesis atmosphere been made up of hydrogen.
  • the synthesis atmosphere will typically comprise a boron containing gas such as diborane at a concentration from equal to or less than 0.01% up to several % by volume.
  • the problem to be solved is what growth parameters to select in order to fabricate synthetic boron doped diamond materials with optimized electrochemical sensing properties. Suitable growth parameters for such boron doped diamond materials have been described in WO2013/135783. However, it has been found that CVD growth parameters should advantageously be changed when growing boron doped diamond materials into trenches in order to achieve void- free filling of the trenches while simultaneously achieving boron doped diamond materials with optimized electrochemical sensing properties. The problem is how to achieve high levels of boron doping while avoiding incorporation of sp2 carbon during growth and also simultaneously ensuring void-free filling of the trenches.
  • a relatively low concentration of carbon containing gas e.g. in a range 0.5%) to 3%o of total gas flow
  • a high power density e.g. 2.8 to 3.8 kW over a 50 mm diameter substrate
  • a relatively high reactor pressure e.g. in the range 120 to 160 Torr (i.e. 16.00 kPa to 21.33 kPa)
  • the substrate temperature has been reduced, the carbon containing gas concentration has been reduced, the power density has been reduced, and the pressure has been reduced.
  • a new parameter space has been found which is capable of achieving void-free boron doped diamond growth into trenches cut in the growth surface of a diamond substrate while also achieving boron doped diamond material which has a high level of boron doping while avoiding incorporation of sp2 carbon during growth.
  • the trenches are filled with boron doped diamond material such that an interface region between the one or more boron doped diamond electrodes and the electrically insulating diamond support matrix comprises no voids having a largest lateral dimension greater than 10 micrometres, 5 micrometres, 1 micrometres, 500 nanometres, 300 nanometres, or 100 nanometres.
  • Such voids can be detected and measured using a microscopic imaging technique such as scanning electron microscopy.
  • the boron doped diamond material over the planar front surface 4 of the electrically insulating diamond substrate 2 is processed back to form a planar sensing surface 12 comprising one or more boron doped diamond electrodes 14 surrounded by an electrically insulating diamond support matrix 16 as illustrated in Figure 1(d).
  • the planar sensing surface 12 advantageously has a surface roughness Ra of no more than 100 nm, 75 nm, 50 nm, 20 nm, or 10 nm after processing. It has been found that the surface finish affects functional performance of the one or more boron doped diamond electrodes 14 in electrochemical sensing applications.
  • the one or more boron doped diamond electrodes 14 extending through the electrically insulating diamond support matrix 16 from the planar sensing surface 12 towards a rear surface 18 of the electrically insulating diamond support matrix with a depth d in a range 20 micrometres to 500 micrometres.
  • the one or more boron doped diamond electrodes 14 may have a depth d of no more than 400 micrometres, 300 micrometres, 200 micrometres, or 100 micrometres, and/or no less than 30 micrometres, 40 micrometres, or 50 micrometres, or any combination of these upper and lower values.
  • a distance D between the planar sensing surface 12 and the rear surface 18 of the electrically insulating diamond support matrix is in a range 50 micrometres to 1.5 mm.
  • the geometry of the structure illustrated in Figure 1(d) is adapted to account for several factors.
  • the depth d is defined such that it is not too shallow so as to reliably process and back contact the electrodes and not too thick that it is difficult to achieve filling via overgrowth without forming voids within the one or more trenches.
  • the distance D should be sufficiently small that vias can reliably be cut through the electrically insulating diamond support matrix 16 to a rear surface of the one or more electrodes 14 in a cost effective manner while being sufficiently large as to provide mechanically robustness to the sensor head structure during fabrication and in use.
  • the diamond sensor head may have a thickness no less than 50 micrometres, 75 micrometres, 100 micrometres, 150 micrometres, or 200 micrometres, and/or no more than 1.5 millimetres, 1 millimetre, 750 micrometres, 500 micrometres, 300 micrometres, or 200 micrometres, or any combination of these upper and lower values.
  • one or more vias 20 are formed extending from the rear surface 18 of the electrically insulating diamond support matrix 16 to the rear surface of the one or more boron doped diamond electrodes 14 within the electrically insulating diamond support matrix as illustrated in Figure 1(e).
  • the vias 20 may be in the form of holes or in the form of elongate trenches. In either case, this step must be carefully controlled to ensure that the vias extend to a rear surface of the one or more boron doped diamond electrodes 14 without extending through the one or more boron doped diamond electrodes 14 to the front sensing surface 12.
  • laser cross-hatching can be used to ensure an even cut during formation of the vias 20 which can ensure that there is no drill-through to the front sensing surface 12.
  • the vias 20 can also aid in providing a relatively uniform ohmic contact at a rear surface of the one or more boron doped diamond electrodes 14 which has a low resistance and/or capacitance.
  • the one or more vias 20 are formed as elongate trenches in one, or a small number, of cutting passes as this provides a cost effective route to fabrication of the vias. In this case, the distance between the rear surface of the electrodes and the rear surface of the electrically insulating diamond support matrix should be sufficiently small that the vias can be formed in this manner.
  • the aspect ratio of the via during cutting provides an indicator as to the quality of the cutting procedure and successful achievement of the ultimate goal to cut a via with a smooth internal surface and which reaches a doped diamond electrodes without punching through to the front sensing surface.
  • the via tends to have a tapered profile as indicated in Figure 1(e) with side walls which are sloped at an angle in a range 30° to 60° relative to a vertical direction perpendicular to the plane of the sensing surface. That said, while such sloped internal walls are typical of a laser cutting technique, if another technique such as an etching technique is utilized to form the vias then the side walls can be substantially vertical.
  • One or more ohmic contacts 22 are formed on the rear surface of the one or more boron doped diamond electrodes 14 within the vias 20 in the electrically insulating diamond support matrix 16.
  • the one or more ohmic contacts 22 within the vias on the rear surface of the one or more boron doped diamond electrodes are formed such that each contact has a resistance which is sufficiently low that an ohmic drop in a faradaic electrochemical experiment is no greater than 10 mV, 8 mV, 6 mV, 4 mV, 2 mV, or 1 mV where the ohmic drop is defined by I x R with I being current and R being total resistance and/or has a resistance per unit area of no more than 10 ⁇ cm " 2 , 8 ⁇ cm “ 2 , 5 ⁇ cm “ 2 , 3 ⁇ cm “ 2 , or 1 ⁇ cm " 2.
  • Calibration is generally required to determine the depth of each laser pass.
  • Hatch direction is decided by geometry; squares or circles can be hatched in multiple directions, rotating the hatch direction with each pass.
  • Long thin shapes can be hatched in a single direction, parallel to the long axis of the shape.
  • Insulating diamond surfaces can be coloured, e.g. with black pen (glass pen). Focussing can then be performed by eye (microscope camera) to the closest 100 ⁇ from the surface.
  • the following laser parameters were utilized in the examples described herein: 1) Power (attenuator): initial pass set in a range 50 - 75% (sufficient to cut but not cause fracturing/blow out) and subsequent passes controlled in a range 20 - 80% (much more flexibility after initial pass).
  • Pulse pitch 3 ⁇ (radius of spot size).
  • F speed Fl - F0.3 (mm/s) (essentially defined by frequency and pulse pitch).
  • the maximum F-speed is limited by acceleration and deceleration of the stage. Generally shapes of size -100 ⁇ will have significant variability in depth at F- speeds > 0.3 mm/s.
  • the one or more ohmic contacts 22 disposed on the rear surface of the one or more boron doped diamond electrodes within the vias in the electrically insulating diamond support matrix may be formed of non-diamond carbon, e.g. graphite. It has been found that the rear surface of the boron doped diamond electrodes can be graphitized using a laser as outlined above and such a non-diamond-carbon surface within the through-hole provides an ohmic contact which is suitable for electrochemical sensor application. Some of the non-diamond- carbon rear contact can be removed by acid cleaning after formation to reduce the resistance of the contact. In this regard, it is advantageous to provide a relatively thin layer of non- diamond carbon for the ohmic contact to present a low resistance contact as described previously.
  • non-diamond carbon e.g. graphite.
  • laser pulsing and optionally cross-hatching can be used to ensure an even cut during laser cutting to form the vias which can ensure that there is no cut-through to the sensing surface and can also aid in providing a relatively uniform and reproducible ohmic contact.
  • other techniques may be used, in a controlled manner, to form suitable trenches 8 and/or vias 20 including, for example, electron beam cutting, ion beam cutting, hot metal dissolution, or plasma etching techniques.
  • the contacts may be formed by a brazing process or using a thermal metal dissolution technique.
  • a thermal sensor can be positioned in front of the planar sensing surface to determine the depth of the cut during formation of the via by taking thermal measurements. This can aid in accurately and reproducibly cutting to a rear surface of the electrodes when forming the vias.
  • the via 20 shown in Figure 1(e) is oriented in a substantially vertical direction, the via can be formed at other angles relative to the planar front sensing surface.
  • one or more electrical connectors 24 are provided extending through the one or more vias to the one or more ohmic contacts 22 disposed on the rear surface of the one or more boron doped diamond electrodes 14 within the vias in the electrically insulating diamond support matrix 16.
  • the one or more electrical connectors 24 may be provided by bonding wires to the contacts 22 or by deposition of an electrically conductive material into the vias 20.
  • Microwave chemical vapor deposition (MW-CVD) polycrystalline insulating synthetic diamond was grown by Element 6 (Harwell, Oxford, UK) in wafer form (25 mm diameter). Typically the substrates were 1 mm in thickness, mechanically lapped (polished) to a surface roughness of ⁇ 2 nm, and then subject to laser micro machining using a high power laser micromachiner (E-355H-3-ATHI-0, Oxford Lasers, UK). The resulting structures were acid cleaned in hot ( ⁇ 200°C) concentrated sulfuric acid saturated with KNO3, to remove any NDC produced during lasering (Wilson et al, J. Phys. Chem. B 2006, 110, 5639-5646).
  • pBDD overgrowths were carried out using MW-CVD on the processed substrates.
  • the approximate growth conditions used to prepare the appropriately doped "metal-like" pBDD films have been described previously (Balmer et al, J. Phys. Cond. Matt. 2009, 21, 364221).
  • Electrical top contacts to pBDD contact pads on the all-diamond electrodes were made by sputtering a Ti/Au (10 nm / 300 nm) layer (Moorfields sputter system, UK) through a KaptonTM tape (DuPont, UK) mask and annealing at 400°C for 5 hrs to produce an ohmic contact (Das et al, Thin Solid Films 1992, 212, 19-24).
  • NDC (graphitized) contacts were made using the laser micromachiner (as described above).
  • Material characterization of the wafers was carried out using optical microscopy (BH-2, Olympus, UK), white light interferometry (Contour GT-K, Bruker, UK), field emission scanning electron microscopy (FE-SEM: Supra 55 VP, Zeiss), atomic force microscopy (AFM: Nano Enviroscope with Nanoscope IV controller, Bruker, UK) and Micro-Raman spectroscopy (Renishaw in Via Raman, Ar + laser at 514.5 nm excitation) using a x50 objective lens and a spot size of ⁇ 5 ⁇ .
  • Electrochemical measurements Electrochemical characterization of the all diamond electrodes was performed in a standard three-electrode configuration using a Pt counter electrode and a reference electrode (saturated calomel electrode, SCE) for solvent window, capacitance and redox electrochemical analysis. CV was carried out using a potentiostat (CHI740a, CH Instruments Inc., USA). The back contacted BDD electrodes were typically mounted into the lid of a polypropylene Falcon tube (Fisher Scientific, UK) using silicone sealant 786 (Dow Corning, UK) or cast in epoxy (RX771C/NC, Robnor, UK) such that the electrode bearing face was exposed to solution. For the top-contacted electrodes the accessible electrode area was defined by epoxy glue or KaptonTM tape. Current-voltage (resistance) curves were measured in air using a Keithley current source (Model 6220, Keithley).
  • All-Diamond Electrode Fabrication The fabrication process employed to produce the all- diamond electrodes is shown in Figures 2 and 3.
  • Figure 2(a) and Figure 3 show the step-by- step fabrication of an all-diamond electrode.
  • the starting substrate, insulating poly crystalline diamond was laser micromachined using a high power laser micromachiner to produce recessed structures "trenches" where the base geometry reflects the resulting electrode geometry.
  • pBDD was overgrown into the lasered trenches and a co-planar structure revealed through multidirectional polishing of the overgrown surface using a resin-bonded scaife embedded with diamond micro-particles, 2 ⁇ - 20 ⁇ in size.
  • FIG. 2(b) shows 3D schematics of different all-diamond pBDD electrodes fabricated using the process illustrated in Figure 2(a) including: (i) dual band; (ii) triple band; (iii) multiple bands; (iv) disk; (v, vi) ring-disk.
  • Figures 2(b)(i, ii and vi) illustrate configurations containing contact pads for top electrical contacts.
  • the minimum feature size is theoretically defined by the minimum laser spot diameter, which for this system is ⁇ 6 ⁇ (Smirnov et al, Anal. Chem. 2011, 83, 7438-43; Kiran et al, Sensors 2012, 12, 7669-81).
  • the entry hole for the laser spot is -20 - 30 ⁇ in diameter as laser fluence (uniformity of energy density across beam diameter) and the ablation threshold of the material are critical.
  • the heterogeneous nature of poly crystalline diamond also means the laser ablation efficiency will vary between grains. It was found that the minimum repeatable feature size on poly crystalline diamond was limited to ca. 50 ⁇ x 50 ⁇ with the laser system employed.
  • Figures 2(c)(i-iii) show typical in-lens and secondary electron FE-SEM images of all- diamond electrode structures produced using the above procedure, including: (i) a triple individually addressable pBDD band electrode (band widths 90 ⁇ , 64 ⁇ and 460 ⁇ ); (ii) 1.02 mm diameter macrodisk electrode and; (iii) a ring-disk pBDD electrode (1.02 mm diameter disk, ring 1.10 mm inner diameter and 1.33 mm outer diameter). Also displayed in Figure 2(c)(iv) is an optical image of a top contacted ring disk electrode where the black electrode structures are clearly visible.
  • FIG. 8 A typical tapping mode AFM image recorded at the boundary between insulating and conducting diamond is shown in Figure 8 (and is discussed in more detail later) for two different pBDD band electrodes (of dimension 0.1 mm x 10 mm and 1 mm x 10 mm).
  • a height line profile taken across the boundary reveals that the pBDD electrode was recessed by approximately 9 nm relative to the insulating region.
  • a very slight recess is expected as the hardness of the pBDD lattice is partially compromised by the presence of boron and so higher doped regions polish slightly faster. This recess is minimal in size compared to those produced using alternative etch-based fabrication processes, which can be several hundreds of nm in size (Smirnov et al, Anal. Chem.
  • R BDD -0.88 ⁇
  • Rcontact is the contact resistance.
  • R CO ntact was determined as 1.7 ⁇ 0.12 ⁇ cm 2 for the Ti/Au contacts.
  • top contacting is electrically back contacting which also means that the entire front face of the all-diamond electrode can be exposed to solution. It has previously been shown that laser micromachining insulating diamond produces a conductive material with electrical properties similar to graphite (Alemanno et al, Diam.Rel. Mat. 2013, 38, 32-35). Back contacting was thus achieved by laser machining a blind hole just through to the rear side of the pBDD electrode, as shown pictorially in the FE-SEM image, Figure 4(a).
  • a plasma is formed at the lasered face; rapid expansion during heating causes most of the diamond to be ablated from the hole in the gaseous oxidized form e.g. CO, C0 2 .
  • a small proportion is however left behind in the form of a black, conductive soot- like deposit, which forms the NDC-conducting diamond contact.
  • most of this material can be removed by an aggressive acid clean if required e.g. when preparing the structure for a pBDD overgrowth.
  • Blind holes were machined by removal of successive ⁇ 30 ⁇ thick layers of insulating diamond using a cross hatching approach, where the direction of the hatch was rotated by 60° with each layer. Rotational cross hatching was employed to ensure an even cut during lasering.
  • the lasered back contact holes were filled with conducting Ag
  • FE-SEM images of cross sectioned back contact holes revealed a tapered structure. For example, drilling 1 mm deep into insulating diamond with a 500 ⁇ diameter entry hole resulted in a base diameter of -300 ⁇ . This is most likely due to sidewalls receiving a lower energy density due to the perpendicular orientation with respect to the beam direction and therefore machining less efficiently.
  • the tapering of the back contact hole is clearly evident in the inset picture to Figure 4(a), showing multiple band structures individually addressed. It is evident from this image that that electrical shorting has not occurred during the contacting procedure.
  • BDD Characterization The all-diamond electrodes where characterized by FE-SEM (as shown in Figure 2(c)), Raman spectroscopy, and electrochemistry i.e. solvent windows, capacitance and CV, the latter for the fast outer sphere one electron transfer redox species, Ru(NH 3 ) 6 3+/2+ .
  • n 18 different electrodes were assessed, including ten band electrodes with width dimensions in the range 50 ⁇ - 1000 ⁇ ; the length was fixed at 10 mm; one dual band electrode (width dimensions 60 ⁇ and 460 ⁇ ); one triple band electrode (width dimensions 64 ⁇ , 90 ⁇ and 460 ⁇ ); one disk electrode of diameter 1.02 mm and two ring-disk electrodes of the dimensions given in Figure 2(c)(iii).
  • the eighteen electrodes fabricated only one was deemed unsuitable for further investigation due to an electrical contact failure; the NDC back contact had partially penetrated through to the front electrode face resulting in a significant increase in the measured capacitance and damage to the electrode surface.
  • Micro-Raman spectroscopy (514.5 nm) is useful for ascertaining NDC and qualitatively assessing boron concentration (Fujishima et al, Diamond Electrochemistry, Elsevier: 2005), however the results must be treated with caution as micro-Raman will only sample a small area of the surface at any one time, spot size depends on optical magnification but typically for x50, spot size is ⁇ 5 ⁇ . Hence either micro-Raman NDC mapping must be undertaken, although this is a very lengthy procedure especially if the electrode is macrosized, or the data must be used in combination with electrochemical analysis.
  • Figure 5(a) shows typical Raman spectra, recorded on both high (black line) and lower doped (red line) facets of the 200 ⁇ wide band electrode and is typical of those recorded on other bands and in other regions of the same electrode.
  • the sp 3 peak which is observed at 1332 cm “1 in undoped polycrystalline diamond, is clearly seen, although has shifted slightly in peak position and decreased in peak intensity, due to the high boron concentration.
  • the asymmetry of the peak (Fano resonance) also reflects the high levels of boron in the lattice, where a Fano resonance is typically observed for boron dopant levels - > 10 20 B atoms cm "3 , which decreases in symmetry the higher the average boron content.
  • Peaks present at -500 cm “1 and -1230 cm “1 are also indicative of the high doping levels. NDC is observed by the presence of broader peaks between 1400 cm “1 and 1600 cm “1 (Prawer et al, Phil. Trans. Royal Soc. A 2004, 362, 2537-2565) and would be more likely to occur in the higher doped regions. We see no evidence of NDC in the Raman spectra recorded.
  • the most effective way of ascertaining NDC is to record CV solvent windows in background electrolyte. Electrochemical analysis samples the entire electrode area and in background electrolyte both capacitive and surface oxidation/reduction processes contribute to the observed CV response. In particular, non-faradaic oxidation of NDC results in an appreciable current flow just before water oxidation. Furthermore, although dissolved oxygen cannot be electrocatalytically reduced on a BDD surface, oxygen is sluggishly reduced in the presence of NDC, resulting in an appreciable cathodic current in the negative window. CVs were recorded at 100 mV s "1 in 0.1 M KNO 3 and are shown for the five band electrodes in the inset to Figure 5(b).
  • the window is featureless until water electrolysis takes place indicative of negligible NDC.
  • solvent windows in the range 3.62 - 3.78 V were recorded (where the anodic and cathodic potential limits are defined as the potential at which a current of 0.4 mA cm "2 is passed for water electrolysis) comparing well with that recorded previously for pBDD grown under similar conditions.
  • the one electrode which contained a surface void showed a notable difference in solvent window characteristics, compared to the other electrodes, as shown in Figure 10.
  • a solvent window of 2.45 V was recorded and clear features were present in the CV, which correlate with the presence of NDC.
  • Capacitance measurements were also used to assess (i) the quality of the pBDD synthesized and (ii) the seal between the pBDD and insulating diamond (poor seals lead to increased capacitance). Note an anomalously high capacitance reading could also indicate a poorly contacted electrode.
  • C d i were determined by cycling at 100 mV s "1 over the potential range ⁇ 0.08 V. Since;
  • C d i can be determined by measuring the charge, Q, at 0 V at a fixed scan rate, v. C d i values 6.61 ⁇ cm “2 (50 ⁇ band); 7.28 ⁇ cm “2 (100 ⁇ band); 6.73 ⁇ cm “2 (200 ⁇ band); 7.70 ⁇ cm “2 (500 ⁇ band) and 5.26 ⁇ cm “2 (1 mm band) were obtained in line with that expected for the boron dopant levels employed during growth.
  • CV was typically performed at 100 mV s "1 in a solution containing 1 mM Ru(NH 3 ) 6 3+ and 0.1 M KN0 3 ; more detailed studies involved varying the scan rate, typically in the range 10 mV s "1 - 500 mV s "1 (as shown in ESI, section 1 , for an all-diamond ring electrode).
  • Figure 5(b) shows the CV characteristics, recorded at 100 mV s "1 for the five band electrodes (solid lines) of different widths.
  • COMSOL as described in ESI, section 1 , was employed to simulate the expected CV response for each electrode (dotted line), assuming diffusion is rate limiting.
  • Low resistance electrical contacting is possible using either Ti/Au top contacts or NDC back contacts, the latter increasing the range of electrode geometries which can be processed and the usability of the resulting electrode, especially in harsh and aggressive environments for long periods of time.
  • the all-diamond electrodes are shown to exhibit the same characteristics of highly doped, negligible NDC content, pBDD grown in bulk form, thus demonstrating that the quality and performance capabilities of the pBDD have not been compromised via growth into the recessed structures.
  • the use of optical grade insulating diamond also paves the wave for combined electrochemical spectroscopic measurements using the same device.
  • a COMSOL (COMSOL multiphysics, COMSOL, SWE) model was employed to simulate the electrochemical CV behavior of the various electrode geometries fabricated as described below.
  • Simulations were performed using the commercial finite element modelling package COMSOL 4.3b (COMSOL AB, Sweden) on a Desktop i7 2700 with 8 GB RAM. Briefly, the structure was defined in the appropriate geometry (disk, ring-disk or band) based upon optical and FE-SEM microscopy measurements of the different electrodes. Due to the different electrode geometries, two approaches were used in the simulations. A full 3D approach was used to simulate the band geometries to accurately represent the behaviour of the ends of the bands. Ring-disk electrodes, which have rotational symmetry, were simulated in a radially symmetric pseudo 3D space. A 2D plane through the radius of the disk was considered, where one boundary was defined as the axis of symmetry of the system.
  • FIG. 6 shows a schematic diagram of a 3D band system.
  • the BDD electrode is labelled surface 1.
  • the insulating diamond surface is labelled 2.
  • the external surfaces of the solution that define the volume are labelled 3.
  • a 2D section has been taken through the 3D model.
  • the identity of the faces is shown on the projected face on the right hand side.
  • the radial model for the ring-disk is also shown, where the ring and disc are labelled la and lb, respectively.
  • the inert diamond surface is boundary 2, the closed volume edge boundaries are labelled 3.
  • the ring-disk system has an additional boundary of axial symmetry that is labelled 4.
  • d (mol cm “3 ) and A represent the concentration and the diffusion coefficient of species i (Ru(NH 3 ) 6 3+/2+ ), (x, y, z) and (r, z) represent the cardinal dimensions of the 3D and 2D axisymmetric systems, respectively, and t is the time.
  • D 8.8 x 10 "6 cm 2 s "1 ).
  • the model was used to simulate the current at the pBDD electrode by solving the diffusion equation for the appropriate geometry subject to the boundary conditions summarized in the table below which includes the set of equations governing flux of species into and out of the domain:
  • k° represents the standard rate of reaction
  • n the number of electrons involved in the reaction
  • a the charge transfer coefficient (assumed to be 0.5)
  • ⁇ the overpotential, which is defined as the applied potential minus the half-wave potential (-0.18 V)
  • T is the temperature (298 K)
  • F and R are the Faraday and Gas constants, respectively.
  • / ec and J z are the current and the flux in the z dimension through the boundary, respectively, and x e i ec , y e i ec and z e i ec are the coordinates that define the electrode area.
  • Figure 5b and Figure 7 show typical experimental CV data matched to simulation.
  • Figure 7 shows experimental (solid lines) and simulated (dashed lines) CVs for an all-diamond BDD ring electrode (as shown in Figure 2(c)(iv)) of 3.10 and 3.20 mm inner and outer diameters, respectively at potential scan rates of 10, 20, 30, 50, 100, 300, and 500 mV s "
  • Figures 8(ai) and 8(bi) show in-lens FE-SEM images of the boundary between the insulating diamond and pBDD for two different band electrodes of width 100 ⁇ (a) and width 1000 ⁇ (b).
  • Figures 8(aii) and 8(bii) show tapping mode AFM images recorded at 20 ⁇ s "1 , the corresponding area is also highlighted on the FE-SEM images, which were taken at an accelerating voltage of 2 kV and a working distance of 5 mm.
  • Height profiles of the surface topography across the insulating diamond-pBDD boundary, as shown in Figures 8(aii) and 8(bii) reveal a height difference of ⁇ 9 nm.
  • Height profiles of the surface topography across grain boundaries in the pBDD region shown in Figures 8(aii) and 8(bii) indicate a height difference of only 1-2 nm.
  • FIGS 9(a) and 9(b) A representative selection of FE-SEM images of all-diamond electrodes is shown in Figures 9(a) and 9(b).
  • Figure 9(a) an individually addressable dual band electrode of width 60 ⁇ and 500 ⁇ , separated by a 40 ⁇ thick layer of electrically insulating diamond is shown. This structure is of use, for example, in generation-collection type electrochemical experiments.
  • Figure 9(b) the boundary region of the BDD 1.02 mm diameter macro electrode is shown, with the grains that grow laterally from the side wall of the insulating diamond trench highlighted. Lateral grain growth can also be seen on each of the bands shown in Figure 9(a), where the smaller band is entirely composed of laterally grown grains whereas the larger band is composed of both laterally and vertically growing grains.
  • a disk electrode of 1.02 mm diameter was electrochemically characterised by: (a) CV with 1 mM Ru(NH 3 ) 6 3+ in 0.1 M KN0 3 ; (b) CV solvent windows in 0.1 M KN0 3 at 100 mV s "1 ; and by Raman spectroscopy as shown in the inset to Figure 11(b).
  • the solvent window is 3.7 V and shows no evidence of 0 2 reduction or NDC oxidation peaks.
  • the Raman which is representative of six spectra recorded on this electrode, shows no evidence of NDC in either light or dark grains.
  • the present specification described how to fabricate optimized electrochemical sensor structures fabricated from diamond materials via techniques involving insulating diamond substrate patterning, boron doped diamond overgrowth, and back contacting techniques. Using the methodology as described herein the following advantageous features can be achieved:

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Abstract

La présente invention concerne une tête de capteur électrochimique en diamant comprenant : une surface de détection plane; une surface arrière à travers laquelle des connexions électriques sont disposées; une ou plusieurs électrodes en diamant dopé au bore qui sont disposées dans des sillons dans une matrice de support de diamant électriquement isolante au niveau de la surface de détection plane, les une ou plusieurs électrodes en diamant dopé au bore s'étendant partiellement à travers la matrice de support de diamant électriquement isolante de la surface de détection plane vers la surface arrière de la matrice de support de diamant électriquement isolante; un ou plusieurs trous de liaison s'étendant depuis la surface arrière de la matrice de support de diamant électriquement isolante à une surface arrière des une ou plusieurs électrodes de diamant dopé au bore dans la matrice de support de diamant électriquement isolante; un ou plusieurs contacts ohmiques disposés sur la surface arrière des une ou plusieurs électrodes de diamant dopé au bore dans les trous de liaison dans la matrice de support de diamant électriquement isolante; et un ou plusieurs connecteurs électriques s'étendant à travers les un ou plusieurs trous de liaison jusqu'aux un ou plusieurs contacts ohmiques disposés sur la surface arrière des une ou plusieurs électrodes de diamant dopé au bore dans les trous de liaison dans la matrice de support de diamant électriquement isolante, la tête de capteur électrochimique en diamant ayant une épaisseur de la surface de détection plane dans laquelle les une ou plusieurs électrodes de diamant dopé au bore sont disposées à la surface arrière de la matrice de support de diamant électriquement isolante dans une plage de 50 micromètres à 1,5 millimètre, les une ou plusieurs électrodes de diamant dopé au bore s'étendant à travers la matrice de support de diamant électriquement isolante de la surface de détection plane à la surface arrière de la matrice de support de diamant électriquement isolante avec une profondeur dans une plage de 20 micromètres à 500 micromètres, et les un ou plusieurs contacts ohmiques dans les un ou plusieurs trous de liaison sur la surface arrière des une ou plusieurs électrodes de diamant dopé au bore ont chacun une résistance qui est suffisamment faible pour qu'une chute ohmique dans un essai électrochimique faradique ne soit pas supérieure à 10 mV, la chute ohmique étant définie par I x R, I étant le courant et R étant la résistance totale.
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CN113523836A (zh) * 2021-06-10 2021-10-22 上海铂世光半导体科技有限公司 一种耐磨导电金刚石定位器
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CN113523836A (zh) * 2021-06-10 2021-10-22 上海铂世光半导体科技有限公司 一种耐磨导电金刚石定位器

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