RU2649040C1 - Infrared sensor with switched sensitive element - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: infrared sensor with a switchable sensing element refers to devices for non-contact temperature measurement in various control and monitoring systems. Infrared sensor with a switchable sensing element comprises a heat receiving membrane attached to the substrate by means of consoles and spaced from the substrate at a distance providing a negligible heat exchange of the membrane to the substrate, temperature-sensitive element with electrical terminals on the consoles and a field electrode that forms the primary circuit of the electrostatic relay with the substrate. Thermosensitive element is a thermocouple with a "warm" junction on the membrane and "cold" contacts on the substrate or a thermistor that form secondary circuits of the relay for signal switching.

EFFECT: increasing sensitivity of the sensor.

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Description

An infrared sensor with a switchable sensing element refers to devices for non-contact temperature measurement in various control and monitoring systems.

Known thermocouple cell on a semiconductor substrate with isolated regions, including a substrate, a groove, a passivating layer deposited on top of the substrate, and an adjacent membrane [1]. The sensor has the following disadvantage: low level of resolution.

Known thermocouple cell, including a substrate, a membrane, a thermocouple, a sacrificial layer deposited on the membrane [2]. A sacrificial layer is created to open part of the membrane by hot junctions of thermocouples. The membrane is deposited on a rigid thermally conductive layer. The sensor has the following disadvantage: low sensitivity.

Known infrared sensor, which includes a substrate, one cantilever beam, one thermocouple and a membrane [3]. The cantilever beam has two pins. The membrane is located above the cantilever beam and fastened to it by a junction. The integrated circuit, which is located under the suspended membrane, is integrated with an infrared sensor. The sensor has the following disadvantages: low resolution and high occupied area on the crystal.

A known sensor consisting of a membrane with a heat-sensitive element, an electromagnetic energy absorber attached to the substrate using conductive busbars [4]. The heat-sensitive element and the electromagnetic energy absorber are combined in one element, which is made in the form of a coating of a thin-film single-crystal material. The sensor has the following disadvantage: high power consumption.

Known infrared sensor, including a heat-receiving membrane, a heat-sensitive element attached directly to the membrane itself, with electrical leads on the consoles with their contacts to the substrate [5]. The sensor has the following disadvantage: low sensitivity. This solution was chosen by us for the prototype.

The problem to which the claimed invention is directed, is to increase the sensitivity of the sensor.

The problem is solved due to the fact that the infrared sensor with a switchable sensing element, containing a heat-receiving membrane attached to the substrate with the help of consoles and located at a distance from the substrate, providing negligible heat exchange of the membrane with the substrate, and a heat-sensitive element attached to the membrane with electrical leads on consoles and their contacts to the substrate, characterized in that the consoles have a field electrode that forms the primary circuit of the electrostatic p For example, a thermosensitive element is a thermocouple with a “warm” junction on the membrane and “cold” contacts on the substrate or a thermistor, one of the disconnected contacts of which, lying on the substrate, is connected to the pn junction and serves as the signal output, and the other is connected to the anti-block junction to the substrate and serves as an ohmic contact to it, and both contacts form secondary relay circuits that serve to switch signals.

Due to the disconnection of the sensitive element from the measuring circuit, the accumulated heat does not “leak” during its accumulation, which helps to increase the sensitivity of the sensor [6].

During heating of the membrane, there is practically no heat leakage from it, and thermo-EMF can be measured by shorting to the measurement circuit.

The time during which the system returns to its equilibrium state is determined by the thermal conductivity of the thermocouple G _t and the specific heat C absorbing the infrared radiation of the MEMS membrane:

When the sensor relaxation time τ _{0 is} less than the frame time τ _k : τ ₀ <τ _k / π, the open circuit voltage

where P is the power of the incident infrared radiation, C is the total heat capacity of the photodetector membrane. Therefore, an increase in the open-circuit voltage using a switched element at a given speed τ _k can make sense at a fairly low frame rate, when due to the high thermal conductivity at a given area of the element, the sensor relaxation time τ << τ _k / π cannot be increased constructively and technologically to a value of ~ τ _k / π.

When using a switchable sensitive element, the length of the console can be significantly reduced so as not to significantly increase the area of the element and realize a sufficiently short mechanical switching time, τ _m << τ _k . This will lead to a decrease in intrinsic noise due to a decrease in resistance. In this case, of course, the length of the thermocouple (thermistor) should provide the cooling time of the membrane along it τ, significantly exceeding the reading time.

The dynamics of thermal and electrical processes is determined by the hierarchy of times τ ₀ , τ, τ ₁ and τ _{p, n} , where τ ₁ is the proper time of thermal relaxation of the console, τ _{p, n} is the time of electrical relaxation in it:

.

.

With the accumulation of heat in the membrane, the cold contacts of the thermocouple do not have direct contact with the substrate and, therefore, the heat exchange of the membrane with the substrate is carried out only through additional supporting consoles of SiO ₂ with thermal conductivity G _c .

до

.In such a situation, when the sensitive element is switched to the substrate in a short time τ, the quasistationary state of the thermocouple is established with the temperature difference ΔT (t) on its junctions and a constant gradient, as a result of which the membrane cools (exponentially) from time τ

before

.

In FIG. 1 shows an infrared sensor with a thermistor switched by a sensitive element, where 1 is a heat-receiving membrane, which acts as a photo-receiving part of infrared radiation; 2 - the substrate is designed to create heterostructures; 3 - consoles are designed to fix the temperature-sensitive element; 4 - thermosensitive element that performs the function of measuring voltage at the electrical terminals 5; 6 - “cold” contacts capable of opening and closing using elastic and electrostatic forces; 7 - field electrode of the primary circuit of the electrostatic relay, which performs the function of a key for closing and opening the circuit; 8 - electrostatic relay with regions 9 performs the function of switching signals: pn junctions and / or pn junction (9a) and anti-blocking (n + -n) junction (9b).

In FIG. 2 shows an infrared sensor with a switchable thermocouple sensing element, where 4a and 4b are shoulders for dissimilar conductors; 10 - warm junction of thermocouples.

When an electric potential of sufficient magnitude is supplied to the field electrode, due to the electrostatic interaction, contacts 6 (Fig. 1 and Fig. 2) come into contact [6].

For an infrared sensor with a switchable sensing element, a thermocouple, the elements of which are made, for example, - a membrane of Si _x Ni _1'-x ; substrate - single-crystal n-Si; consoles - SiO ₂ , thermocouple - polycrystalline Si; “Cold” contacts, “warm” junction and field electrode - Al.

For an infrared sensor with a switchable sensing element, a thermistor, the elements of which are made, for example, an α-Si membrane; substrate - single-crystal n-Si; consoles - SiO ₂ ; thermistor - from polycrystalline Si; “Cold” contacts, “warm” junction and field electrode - Al.

Since the thermal conductivity coefficient of SiO _{2 is} approximately 30 times lower than the thermal conductivity coefficient Si *, then, for example, with a console SiO ₂ length of 100 μm, a width of 2 μm, and a thickness of 0.5 μm with a photodetector membrane area of 5000 μm ² τ ₀ ≈1 s . Therefore, at τ _k > 3, using a switchable sensitive element and a SiO ₂ cantilever, it would be possible to obtain an open circuit voltage 30 times higher, ceteris paribus, the open circuit voltage with an element on the same Si * cantilever: the relaxation time of such a sensor is τ≈ 0.03 s.

For a thermocouple with a length l = 10 μm:

, τ_р,n≈l²/D≈10^-7 c (D_Si*≈10 см²/с).τ ₀ ≈1 s, τ≈τ ₀ / 300≈0.003 s,

, τ _{p, n} ≈l ² / D≈10 ^-7 s (D _{Si *} ≈10 cm ² / s).

Thus, vacuum infrared photodetectors with a switchable sensing element can be quite effective for thermal imaging systems.

Information sources

1. US Patent No. 9324760

2. European patent No. 2887032

3. US Patent No. 6,335,478

4. RF patent No. 2511275

5. US Patent No. 2014326883 - prototype

6. Fedirko V.A., Fetisov E.A. Electromechanics TIR MEMS. // Proceedings of the First Russian-Belarusian conference "Elemental base of domestic radio electronics." RNTORES them. A.S. Popova, Nizhny Novgorod. 2013.Vol. 2.P. 13-16.

7. Fetisov E.A., Fedirko V.A., Timofeev A.E. Investigation of a thermal infrared photodetector on a vacuum micro / nanoelectromechanical system with non-stationary thermoelectric effect. ACTUAL PROBLEMS OF ELECTRONIC INSTRUMENT. APEP-2016. Saratov. 2016.Vol. 2.P. 590-596.

Claims (1)

An infrared sensor with a switchable sensing element, comprising a heat-receiving membrane attached to the substrate by means of consoles and located at a distance of no more than its thickness from the substrate, and a heat-sensitive element attached to the membrane with electrical terminals on the consoles and their contacts to the substrate, characterized in that the consoles have a field electrode that forms the primary circuit of the electrostatic relay with the substrate, the thermosensitive element is a thermocouple with a “warm” junction on the membrane and “Cold” contacts on the substrate or a thermistor forming secondary relay circuits for switching signals.

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