MEMS infrared detector with ambient temperature crosstalk suppression and control method thereof

Abstract

The present application relates to a kind of MEMS infrared detector with ambient temperature crosstalk suppression and its control method, belong to MEMS infrared sensing technical field.Infrared detector includes substrate, suspended film is connected to substrate by several outer support beam, suspended film is at least divided into a hot end island region and a cold end island region inside, and hot end island region and cold end island region are connected by inner support beam;Main detection thermocouple, by several pairs of first thermocouple series connection, and the hot junction of each first thermocouple is arranged in hot end island region, and the cold junction of first thermocouple is arranged in cold end island region;Infrared absorption layer, is arranged above hot end island region;Peltier refrigeration unit, by several pairs of second thermocouple, and the cold junction of second thermocouple is arranged in cold end island region, and the hot junction of second thermocouple is arranged in the heat sink region of substrate;Cold end temperature sensor is integrated in cold end island region, and closed loop control circuit is electrically connected with cold end temperature sensor and Peltier refrigeration unit.

Description

Technical Field

[0001] This invention relates to a MEMS infrared detector with ambient temperature crosstalk suppression and its control method, belonging to the field of MEMS infrared sensing technology. Background Technology

[0002] MEMS thermopile infrared detectors operate based on the Seebeck effect: they consist of multiple thermocouples connected in series. The hot end absorbs infrared radiation, generating a temperature rise, while the cold end is anchored to a silicon substrate as a temperature reference. The temperature difference between the hot and cold ends is converted into a voltage signal output. These devices can operate at room temperature, are passive with low power consumption, are small in size, and are low in cost, making them the mainstream infrared sensing solution for consumer electronics and industrial inspection.

[0003] The inherent drawback of thermopile is that the output voltage only reflects the relative temperature difference between the hot and cold ends and cannot directly correspond to the absolute power of the incident infrared radiation. When the ambient temperature fluctuates, the temperature of the cold end changes synchronously with the substrate, which directly causes the output zero point to drift. This is the core factor restricting the detection accuracy and long-term stability.

[0004] To address this issue, conventional methods typically include: using a high-precision ambient temperature sensor for software compensation, or using an external thermoelectric cooler (TEC) for temperature control of the entire detector. However, software compensation is limited by the temperature gradient and response delay between the sensor and the cold junction, making it difficult to accurately track transient environmental fluctuations. External TEC solutions, on the other hand, are bulky, consume a lot of power, and introducing additional thermal noise by cooling the entire chip, thus negating the miniaturization and low power consumption advantages of MEMS devices. Furthermore, existing Chinese patent document CN112113670A discloses a MEMS thermopile infrared detector and its fabrication method, which attempts to actively heat the cold junction region by integrating a heater and forming a feedback control loop with a temperature sensor to keep the cold junction region constant at a certain operating temperature point higher than the ambient temperature. This type of solution can suppress the impact of ambient temperature fluctuations on the cold junction to a certain extent. However, it has the following inherent limitations: On the one hand, since the operating temperature is higher than the ambient temperature, the heater needs to continuously inject heat into the cold junction region to maintain the temperature difference, resulting in high power consumption; on the other hand, the heater itself, as an additional heat source, will introduce additional thermal noise into the chip, interfering with the detection accuracy. In addition, the isothermal control of this type of solution relies on dynamic feedback adjustment. When the ambient temperature changes rapidly or encounters a large thermal shock, the heater needs to significantly adjust its power to track temperature fluctuations, and the response delay and power consumption of the control system face severe challenges. At the same time, since the temperature of the cold junction region is always higher than the ambient temperature, the temperature difference between the cold junction region and the environment decreases as the ambient temperature rises, and the stability margin of the isothermal control system decreases as the ambient temperature rises, which seriously limits the applicability of the detector in wide temperature range scenarios.

[0005] Therefore, there is an urgent need to develop a MEMS thermopile detector that can actively suppress ambient temperature crosstalk inside the chip, while avoiding inherent defects such as additional thermal noise and insufficient control margin under high temperature conditions. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a MEMS infrared detector with ambient temperature crosstalk suppression and its control method, which solves the problem that the output baseline of existing thermopile detectors is easily affected by ambient temperature fluctuations, and improves measurement accuracy and stability without introducing additional power consumption and thermal noise.

[0007] The technical solution of the present invention is as follows: A MEMS infrared detector with ambient temperature crosstalk suppression includes: Substrate, with an insulating cavity at the bottom; A suspended thin film is connected to a substrate by several external support beams. The interior of the suspended thin film is divided into at least one hot-end island region and one cold-end island region, which are connected by internal support beams. The main detection thermopile consists of several pairs of first thermocouples connected in series. The hot junction of each first thermocouple is located in the hot end island region, and the cold junction of the first thermocouple is located in the cold end island region. An infrared absorption layer is disposed above the hot-end island area and is thermally coupled to the first thermocouple junction. The integrated miniature Peltier cooling unit consists of several pairs of second thermocouples. The cold junction of the second thermocouple is located in the cold end island region, and the hot junction of the second thermocouple is located in the heat sink region of the substrate. The heat sink region is the part of the substrate excluding the insulating cavity, that is: substrate = insulating cavity part + heat sink part. The cold end temperature sensor is integrated into the cold end island area and is used to measure the actual temperature of the cold end island area in real time. The closed-loop control circuit is electrically connected to the cold-end temperature sensor and the Peltier refrigeration unit.

[0008] According to a preferred embodiment of the present invention, the cold-end island region is connected to the hot-end island region via an inner support beam and to the substrate anchor point via an outer support beam. This design ensures that the area at the connection between the cold-end island region, the hot-end island region, and the substrate, excluding the inner and outer support beams, is open. This minimizes the total heat leakage from the cold-end island region to the substrate and the hot-end island region, guaranteeing that the Peltier cooling unit can cool and maintain the temperature with minimal power consumption. T set The substrate anchor point refers to the fixed connection point (i.e., mechanical support column / contact point) between the suspended thin film (200) and the fixed substrate (100) below.

[0009] According to a preferred embodiment of the present invention, the main detector thermopile and the Peltier cooling unit use the same thermoelectric material combination, and the two are prepared and formed simultaneously. The thermoelectric material combination is a combination of n-type polycrystalline silicon and p-type polycrystalline silicon.

[0010] According to a preferred embodiment of the present invention, both the inner support beam and the outer support beam use a SiO2 / Si3N4 composite dielectric film as a mechanical support layer.

[0011] According to a preferred embodiment of the present invention, the cold junction temperature sensor is a platinum thin film resistor or a polycrystalline silicon resistor.

[0012] According to a preferred embodiment of the present invention, the infrared absorption layer is a porous metal layer of gold black or platinum black or a multilayer dielectric absorption film, and the infrared detector is vacuum-encapsulated or atmospheric pressure-encapsulated, with an infrared transmission window corresponding to the detection band provided on the top of the encapsulation.

[0013] According to a preferred embodiment of the present invention, the closed-loop control circuit includes a temperature readout module, an error comparator, and a programmable drive unit connected in sequence.

[0014] A control method for a MEMS infrared detector with ambient temperature crosstalk suppression, comprising the following steps: The temperature readout module connects to the cold junction temperature sensor and outputs the current cold junction temperature value. An error calculator compares the current temperature value with a preset reference temperature. T set The difference in temperature is used by the programmable drive unit to generate a cooling drive current, which is then applied to the Peltier cooling unit to adjust its cooling power, forming a negative feedback closed loop. This keeps the temperature of the cold end island area constant at a preset reference temperature lower than the ambient temperature. T set The above isolates the effect of ambient temperature fluctuations on the cold junction of the first thermocouple, ensuring that the output voltage baseline of the main probe thermopile depends only on this controlled constant temperature. T set .

[0015] According to a further preferred embodiment of the present invention, a preset reference temperature T set The ambient temperature is at least 5°C lower than the minimum operating temperature of the infrared detector to ensure that the cooling unit always operates in heat absorption mode without the need for bidirectional current switching.

[0016] The beneficial effects of this invention are as follows: 1. Eliminate ambient temperature crosstalk at the source: By actively maintaining the temperature of the cold junction island area at a preset value lower than the ambient temperature, ambient temperature fluctuations no longer directly affect the cold junction temperature. The DC output baseline of the detector is highly stable, which greatly improves the long-term stability and temperature resolution in DC applications such as non-contact temperature measurement and gas detection.

[0017] 2. Full MEMS process compatibility, without increasing additional manufacturing costs: The Peltier cooling unit and cold end temperature sensor can be completed in the same process as the main probe thermopile using the same polycrystalline silicon thin film process. Only the layout design needs to be modified, without the need for additional materials or complex heterogeneous integration.

[0018] 3. Low power consumption and miniaturization: Microwatt-level active cooling is performed only on the cold end island area with extremely small heat capacity, resulting in power consumption far lower than that of external TEC solutions, while retaining the miniaturization advantages of MEMS devices.

[0019] 4. No software compensation delay required: The cold junction is directly stabilized through a physical constant temperature closed loop. The response speed depends on the closed loop control bandwidth, which is much faster than software compensation schemes that rely on external temperature sensors. This can effectively suppress transient environmental temperature shocks. Attached Figure Description

[0020] Figure 1 This is a cross-sectional structural diagram of the present invention.

[0021] Figure 2 This is a top view of the structure of the present invention.

[0022] Figure 3 This is a block diagram illustrating the closed-loop constant temperature control principle of the present invention.

[0023] Among them, 100 is the substrate; 101 is the thermal insulation cavity; 102 is the substrate anchor point; 200 is the suspended thin film; 201 is the hot end island area; 202 is the cold end island area; 203 is the inner support beam; 204 is the outer support beam; and 300 is the infrared absorption layer. 401. Main detection thermopile; 401a. First thermocouple hot junction; 401b. First thermocouple cold junction; 402, Peltier refrigeration unit; 402a, cold junction of the second thermocouple; 402b, hot junction of the second thermocouple; 403. Cold end temperature sensor. Detailed Implementation

[0024] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto. Example

[0025] like Figures 1-3 As shown, this embodiment provides a MEMS infrared detector with ambient temperature crosstalk suppression, including: Substrate 100, with an insulating cavity 101 at its bottom; The suspended film 200 is connected to the substrate by several external support beams 204. The interior of the suspended film 200 is divided into at least a hot end island region and a cold end island region. The hot end island region 201 and the cold end island region 202 are connected by internal support beams. The main detection thermopile is composed of several pairs of first thermocouples connected in series. The hot junction 401a of each first thermocouple is located in the hot end island region 201, and the cold junction 401b of the first thermocouple is located in the cold end island region 202. An infrared absorption layer 300 is disposed above the hot end island region 201 and is thermally coupled to the first thermocouple junction 401a. The integrated miniature Peltier cooling unit 402 is composed of several pairs of second thermocouples. The cold junction 402a of the second thermocouple is disposed in the cold end island region 202, and the hot junction 402b of the second thermocouple is disposed in the heat sink region of the substrate 100. The heat sink region is the part of the substrate excluding the insulating cavity, that is: substrate = insulating cavity part + heat sink part. The cold end temperature sensor 403 is integrated into the cold end island area 202 and is used to measure the actual temperature of the cold end island area in real time. The closed-loop control circuit is electrically connected to the cold-end temperature sensor 403 and the Peltier refrigeration unit 402.

[0026] The cold-end island region is connected to the hot-end island region via an inner support beam and to the substrate anchor point via an outer support beam. The areas connecting the cold-end island region to the hot-end island region and the substrate, excluding the inner and outer support beams, are hollowed out. This ensures that the total heat leakage from the cold-end island region to the substrate and hot-end island region is sufficiently small, guaranteeing that the Peltier cooling unit can cool and maintain the temperature with minimal power consumption. T set The substrate anchor point refers to the fixed connection point (i.e., mechanical support column / contact point) between the suspended thin film 200 and the fixed substrate 100 below.

[0027] The main detector thermopile and the Peltier cooling unit use the same thermoelectric material combination, and both are fabricated and formed simultaneously. The thermoelectric material combination is a combination of n-type polycrystalline silicon and p-type polycrystalline silicon.

[0028] Both the inner and outer support beams use SiO2 / Si3N4 composite dielectric thin film as the mechanical support layer.

[0029] The cold junction temperature sensor is a platinum thin film resistor or a polycrystalline silicon resistor.

[0030] The infrared absorption layer 300 is a porous metal layer of gold black or platinum black or a multilayer dielectric absorption film. The infrared detector is vacuum-encapsulated or atmospheric pressure-encapsulated, and the top of the encapsulation is provided with an infrared transmission window corresponding to the detection band.

[0031] The closed-loop control circuit includes a temperature readout module, an error comparator, and a programmable drive unit connected in sequence.

[0032] A control method for a MEMS infrared detector with ambient temperature crosstalk suppression, comprising the following steps: The temperature readout module connects to the cold junction temperature sensor and outputs the current cold junction temperature value. An error calculator compares the current temperature value with a preset reference temperature. T set The difference in temperature is used by the programmable drive unit to generate a cooling drive current, which is then applied to the Peltier cooling unit to adjust its cooling power, forming a negative feedback closed loop. This keeps the temperature of the cold end island area constant at a preset reference temperature lower than the ambient temperature. T set The above isolates the effect of ambient temperature fluctuations on the cold junction of the first thermocouple, ensuring that the output voltage baseline of the main probe thermopile depends only on this controlled constant temperature. T set .

[0033] Preset reference temperature T set The ambient temperature is at least 5°C lower than the minimum operating temperature of the infrared detector to ensure that the cooling unit always operates in heat absorption mode without the need for bidirectional current switching.

Claims

1. A MEMS infrared detector with ambient temperature crosstalk suppression, characterized in that, include: Substrate, with an insulating cavity at the bottom; A suspended thin film is connected to a substrate by several external support beams. The interior of the suspended thin film is divided into at least one hot-end island region and one cold-end island region, which are connected by internal support beams. The main detection thermopile consists of several pairs of first thermocouples connected in series. The hot junction of each first thermocouple is located in the hot end island region, and the cold junction of the first thermocouple is located in the cold end island region. An infrared absorption layer is disposed above the hot-end island area and is thermally coupled to the first thermocouple junction. The Peltier cooling unit consists of several pairs of second thermocouples. The cold junction of the second thermocouple is located in the cold end island region, and the hot junction of the second thermocouple is located in the heat sink region of the substrate. The heat sink region is the part of the substrate excluding the insulating cavity. The cold end temperature sensor is integrated into the cold end island area and is used to measure the actual temperature of the cold end island area in real time. The closed-loop control circuit is electrically connected to the cold-end temperature sensor and the Peltier refrigeration unit.

2. The MEMS infrared detector with ambient temperature crosstalk suppression as described in claim 1, characterized in that, The cold end island area is connected to the hot end island area through an inner support beam and to the substrate anchor point through an outer support beam, so that the area at the connection between the cold end island area, the hot end island area and the substrate, except for the inner support beam and the outer support beam, is hollowed out.

3. The MEMS infrared detector with ambient temperature crosstalk suppression as described in claim 2, characterized in that, The main detector thermopile and the Peltier cooling unit use the same thermoelectric material combination, and both are fabricated and formed simultaneously. The thermoelectric material combination is a combination of n-type polycrystalline silicon and p-type polycrystalline silicon.

4. The MEMS infrared detector with ambient temperature crosstalk suppression as described in claim 3, characterized in that, Both the inner and outer support beams use SiO2 / Si3N4 composite dielectric thin film as the mechanical support layer.

5. The MEMS infrared detector with ambient temperature crosstalk suppression as described in claim 4, characterized in that, The cold junction temperature sensor is a platinum thin film resistor or a polycrystalline silicon resistor.

6. The MEMS infrared detector with ambient temperature crosstalk suppression as described in claim 5, characterized in that, The infrared absorption layer is a porous metal layer of gold black or platinum black or a multilayer dielectric absorption film. The infrared detector is vacuum-encapsulated or atmospheric pressure-encapsulated, and the top of the encapsulation is provided with an infrared transmission window corresponding to the detection band.

7. The MEMS infrared detector with ambient temperature crosstalk suppression as described in claim 6, characterized in that, The closed-loop control circuit includes a temperature readout module, an error comparator, and a programmable drive unit connected in sequence.

8. The control method for a MEMS infrared detector with ambient temperature crosstalk suppression as described in claim 7, characterized in that, The steps are as follows: The temperature readout module connects to the cold junction temperature sensor and outputs the current cold junction temperature value. An error calculator compares the current temperature value with a preset reference temperature. T set The difference in temperature is used by the programmable drive unit to generate a cooling drive current, which is then applied to the Peltier cooling unit to adjust its cooling power, forming a negative feedback closed loop. This keeps the temperature of the cold end island area constant at a preset reference temperature lower than the ambient temperature. T set The above isolates the effect of ambient temperature fluctuations on the cold junction of the first thermocouple, ensuring that the output voltage baseline of the main probe thermopile depends only on this controlled constant temperature. T set .

9. The control method for a MEMS infrared detector with ambient temperature crosstalk suppression as described in claim 8, characterized in that, Preset reference temperature T set The ambient temperature is at least 5°C lower than the minimum operating temperature of the infrared detector to ensure that the cooling unit always operates in heat absorption mode without the need for bidirectional current switching.

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