CMOS-MEMS monolithic integrated thermopile infrared detector with thermal decoupling structure
By designing a thermodecoupled structure in the CMOS-MEMS monolithic integrated thermopile infrared detector, including thermal insulation cavity, heat dissipation microflower and thermal isolation tank, the impact of ASIC self-heating effect on the thermopile is solved, and higher measurement accuracy and stability are achieved.
Patent Information
- Application Number
- CN202510068706.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-16
- Publication Date
- 2025-04-25
AI Technical Summary
Under the ASIC self-heating effect, the CMOS-MEMS monolithic integrated thermopile infrared detector leads to inhomogeneous temperature changes and response characteristics of the thermopile, affecting measurement accuracy and stability.
Design a CMOS-MEMS monolithic integrated thermopile infrared detector with a thermodecoupled structure, including a MEMS thermopile, ASIC circuit and a thermodecoupled structure. Thermal decoupling structure includes a thermal insulation cavity, a heat dissipation microflower and a thermal isolation tank to reduce the impact of ASIC self-heating effect on the thermopile.
Through the differential structure thermopile and the ASIC circuit optimized by the thermal layout, heat is evenly distributed, and heat dissipation is accelerated through the microflow channel and thermal isolation tank, which significantly reduces the thermal interference of the ASIC circuit on the MEMS thermopile and improves the measurement accuracy and stability of the detector.
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Figure CN119873723A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the field of CMOS-MEMS chips, in particular to a CMOS-MEMS monolithic integrated thermopile infrared detector with a thermal decoupling structure. Background Art
[0002] As a non-contact temperature measurement method, thermopile infrared detection technology achieves accurate determination of the surface temperature of an object by measuring the temperature difference caused by infrared radiation. With its advantages such as high sensitivity, fast response and wide range, it has shown important value in many fields.
[0003] At present, CMOS-MEMS monolithic integrated thermopile infrared detectors based on CMOS technology are being widely studied due to their high reliability and high cost performance. One of the main problems it faces is the influence of ASIC self-heating on thermopile infrared sensors. Since the ASIC chip generates a certain amount of heat during operation, this heat may be transferred to the thermopile, causing the temperature of the thermopile to change, thereby affecting its measurement accuracy and stability. In addition, the self-heating of the ASIC chip will also cause local temperature gradients, causing the response characteristics of the thermopile to change non-uniformly, further reducing the performance of the sensor; therefore, a CMOS-MEMS monolithic integrated thermopile infrared detector with a thermal decoupling structure is urgently needed to reduce the influence of the ASIC self-heating effect on the infrared thermopile detector.
[0004] The working principle of CMOS-MEMS monolithic integrated thermopile infrared detector is based on the Seebeck effect, that is, in a closed loop composed of two different conductors or semiconductors (that is, forming a thermocouple), when the temperatures of the two contact points are different, a thermoelectric potential will be generated in the loop, and the thermocouples can be connected in series to form a thermopile. In practical applications, the reason why multiple thermocouples are connected in series to form a thermopile is to increase the total thermoelectric potential, thereby increasing the sensitivity of the detector for direct measurement. CMOS-MEMS monolithic integrated thermopile infrared detector is different from the traditional thermopile detector in which the circuit and the thermopile are separated independently. It is compatible with CMOS technology, and uses the polysilicon layer and metal layer in the CMOS process to form a thermopile structure after graphic design, and is integrated with the AS IC circuit on the same wafer, and then a single-chip integrated structure is formed by dicing. This integration method makes it more reliable, reduces the signal attenuation caused by metal leads, and the manufacturing cost is greatly reduced by using the same wafer. However, its disadvantage is that the influence of ASIC self-heating effect on infrared thermopile detector will be aggravated when monolithic integration is carried out without corresponding thermal decoupling structure. Summary of the invention
[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and to propose a CMOS-MEMS monolithic integrated thermopile infrared detector with a thermal decoupling structure, which can greatly reduce the influence of ASIC self-heating on the performance of the thermopile infrared detector.
[0006] In order to achieve the above object, the technical solution specifically adopted by the present invention is as follows:
[0007] A CMOS-MEMS monolithic integrated thermopile infrared detector with a thermal decoupling structure includes a MEMS thermopile, an ASIC circuit and a thermal decoupling structure; the MEMS thermopile includes a thermopile I and a thermopile II, and the infrared absorption efficiency of the thermopile I and the thermopile II are different; the thermal decoupling structure includes a thermal insulation cavity located at the back of the MEMS thermopile, a heat dissipation microchannel located below the ASIC circuit, and a thermal isolation groove located between the MEMS thermopile and the ASIC circuit, wherein the thermopile I and the thermopile II share the same thermal insulation cavity, which is used to reduce the heat dissipation of the hot end from the bottom of the substrate, thereby increasing the temperature difference electromotive force between the cold end and the hot end, and preventing the heat generated by the self-heating effect of the ASIC from being conducted to the MEMS thermopile through the lower body silicon part. The heat dissipation microchannel is used to dissipate the heat generated by the ASIC through the microchannel and transmit it to the outside of the chip. The thermal isolation groove is used to thermally isolate the ASIC circuit from the MEMS thermopile and reduce the heat generated by the ASIC from being transmitted to the MEMS thermopile through thermal conduction.
[0008] Furthermore, the MEMS thermopile is a MEMS thermopile chip formed on the front side of a single crystal silicon wafer by a CMOS process. The main body presents a differential structure and is composed of a thermopile I and a thermopile II with highly symmetrical structures. Both the thermopile I and the thermopile II include structures such as thermocouples, tungsten through-holes, and infrared absorption layers. The polysilicon layer and the metal layer of the thermocouple are connected by tungsten through-holes and are connected in series after photolithography patterning to form a thermopile. The thermopile I and the thermopile II are in the same horizontal plane and are arranged vertically. The infrared absorption layer of the thermopile II adopts a thin film with high infrared reflectivity, while the infrared absorption layer of the thermopile I adopts a silicon nitride passivation layer in the CMOS process.
[0009] Furthermore, the ASIC circuit is prepared on a single crystal silicon wafer using a standard CMOS process, and is composed of a differential operational amplifier module (Amp l ifi er), an analog-to-digital converter (ADC), an on-chip temperature sensor (Temperature sensor), a reference voltage module (Vo l tage Reference) and a microcontroller module (MCU). The module with high power consumption is placed in the central position, and the modules with low power consumption are evenly distributed at both ends, so that the heat of the ASIC circuit is distributed as evenly as possible so that the individual thermopiles in the differential structure thermopile are subject to the same degree of thermal interference.
[0010] Furthermore, the differential operational amplifier module is mainly used to make the difference between the output thermoelectric potentials of thermopile I and thermoelectric pile II and to amplify them appropriately to eliminate the thermoelectric potential caused by the self-heating effect of the AS IC; the analog-to-digital converter is used to convert the analog output thermoelectric potential into a digital signal and transmit it to the microcontroller MCU module for subsequent processing; the on-chip temperature sensor is used to monitor the cold end temperature of the thermopile.
[0011] The present invention has the following characteristics and beneficial effects:
[0012] The present invention eliminates the influence of ASIC self-heating effect on MEMS thermopile to a great extent from three aspects. First, different from the traditional single-ended thermopile, a differential structure thermopile is designed, which usually removes the thermal interference of ASIC circuit by differential method. Then, by adopting the ASIC circuit with optimized thermal layout, the heat is evenly distributed. Finally, the designed microchannel and thermal isolation groove structure accelerates the dissipation of ASIC circuit heat, cuts off the heat conduction path with the thermopile, and further reduces the thermal interference of ASIC circuit on MEMS thermopile. BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Figure 1 A schematic diagram of a CMOS-MEMS monolithic integrated thermopile in an embodiment of the present invention;
[0014] Figure 2 A side cross-sectional view of a CMOS-MEMS monolithic integrated thermopile infrared detector with a thermal decoupling structure according to an embodiment of the present invention;
[0015] Figure 3 A top view of a CMOS-MEMS monolithic integrated thermopile infrared detector with a thermal decoupling structure according to an embodiment of the present invention;
[0016] Figure 4 is a differential thermopile circuit equivalent model in an embodiment of the present invention;
[0017] In the figure: 1. MEMS thermopile; 2. ASIC circuit; 3. Thermal decoupling structure; 1-1. Thermocouple polysilicon layer; 1-2. Thermocouple metal layer; 1-3. Tungsten through hole at the hot end of the thermopile; 1-4. Tungsten through hole at the cold end of the thermopile; 1-5. Metal electrode; 3-1. Thermal insulation cavity; 3-2. Thermal insulation groove; 3-3. Microfluidic channel. DETAILED DESCRIPTION
[0018] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.
[0019] In order to reduce the influence of ASIC self-heating on the performance of thermopile infrared detector, the present invention provides a CMOS-MEMS monolithic integrated thermopile infrared detector with a thermal decoupling structure, which is mainly divided into three parts: MEMS thermopile 1, ASIC circuit 2 and thermal decoupling structure (mainly on the back side). Figure 1 Not marked), in the overall layout, the MEMS thermopile 1 is a differential structure composed of thermopile I and thermopile II. Thermopile I and thermopile II have different infrared absorption rates to eliminate the influence of the self-heating effect of the AS IC circuit. The ASIC circuit and the MEMS thermopile are on the right side of the AS IC, and the chip self-heating concentrated area is deployed in the center. The thermal insulation structure is mainly distributed on the back, cutting off the heat conduction path between the ASIC circuit and the MEMS thermopile, further reducing the thermal interference of the AS IC circuit on the MEMS thermopile.
[0020] More specifically, the structure is Figure 2 and Figure 3 As shown, the first part is a MEMS thermopile 1, which is prepared on the front side of single crystal silicon by standard CMOS process, including a thermocouple with a strip structure, a tungsten through hole, an infrared absorption layer and a metal electrode 1-5. Among them, the thermocouple is composed of a polysilicon layer 1-1 and a metal layer 1-2, and the two are connected through a tungsten through hole 1-3 at the hot end of the thermopile and a tungsten through hole 1-4 at the cold end of the thermopile, and are connected in series after photolithography patterning to form a thermopile. The thermopile I and the thermopile II are on the same horizontal plane and arranged vertically, sharing the same thermal insulation cavity 3-1, and the only difference is that the infrared absorption area is different, that is, the infrared absorption efficiency is different. After the entire CMOS process is completed, a layer of high infrared reflectivity film is deposited on the thermopile II, which greatly reduces the infrared absorption rate, and the infrared absorption film of the thermopile I is played by the silicon nitride passivation layer in the CMOS process. The difference in the infrared absorption rate of the two thermopiles can be obtained through later calibration. By subtracting the output thermoelectromotive force of the two thermopiles, the influence of AS IC self-heating can be greatly reduced.
[0021] The second part is ASIC circuit 2, Figure 3The top view of the CMOS-MEMS monolithic integrated thermopile with thermal decoupling structure. The ASIC circuit 2 is prepared on a single crystal silicon wafer by standard CMOS process, and is composed of a differential subtraction module, an analog-to-digital converter, an on-chip temperature sensor, a signal interface module and a microcontroller MCU module. The differential subtraction module is mainly used to make a difference between the output and thermoelectric potential of thermopile I and thermopile II to eliminate the thermoelectric potential caused by the self-heating effect of ASIC. The analog-to-digital converter is used to convert the analog output thermoelectric potential into a digital signal and transmit it to the microcontroller MCU module through the signal interface module for subsequent processing. The on-chip temperature sensor is used to monitor the cold end temperature of the thermopile. When laying out the ASIC, attention should be paid to deploying modules with relatively high heat generation, that is, high power consumption, in the central area of the ASIC area, and the overall heat generation should be symmetrical, so as to ensure that the influence of the ASIC self-heating effect on thermopile I and thermopile II is consistent as much as possible.
[0022] The third part is the thermal decoupling structure, which consists of the thermal insulation cavity 3-1 on the back of the MEMS thermopile, the isolation groove 3-2 on the upper surface of the chip, and the heat dissipation microchannel 3-3 on the back of the AS IC. All three are etched by dry etching technology after the chip is made by the standard CMOS process. The isolation groove is mainly to cut off the main heat conduction path between the AS IC circuit and the MEMS thermopile, so that even if the AS IC fails to achieve a thermally symmetrical layout, it can minimize the inconsistent impact of uneven heat generation on thermopile I and thermopile II. The thermal insulation cavity on the back of the MEMS thermopile is mainly used to increase the temperature difference between the cold end and the hot end. The hot end is located on the supporting film above the thermal insulation cavity, while the cold end is located on the bulk silicon outside the thermal insulation cavity. Therefore, when the thermopile absorbs infrared radiation, the temperature of the hot end rises, while the temperature of the cold end remains basically unchanged, consistent with the bulk silicon, thereby increasing the temperature of the hot end and the cold end, thereby increasing the output thermoelectric potential. In addition, it also helps to reduce the inconsistent impact of ASIC's uneven heat generation on thermopile I and thermopile II, because the insulation cavity removes the bulk silicon and cuts off part of the heat conduction path between ASIC and MEMS. It is worth noting that the thickness of the back cavity should be appropriate. If it is too deep, the support film is easily damaged, and if it is too shallow, the insulation effect is reduced. Generally, the top of the cavity is about 1um away from the thermocouple layer. When the self-heating effect of the ASIC circuit is not serious, there is no need to add microchannels. When the power consumption of the ASIC circuit is high and the self-heating effect is serious, microchannels can be added to dissipate the heat generated by the ASIC in time. The production of microchannels first uses deep reactive ion etching to etch a narrow gap on the silicon substrate, and then uses an isotropic dry etching process to widen the width of the gap in the silicon substrate, which is filled with a condenser (deionized water). The heat generated by the ASIC above is dissipated by the flow of the condenser (deionized water) in the microchannel.
[0023] Figure 4 This is the equivalent circuit diagram of the thermopile. The thermopile I in the differential structure thermopile can be equivalent to the thermoelectromotive force V generated by the self-heating of the AS IC. ASIC The circuit is composed of a thermoelectric potential V1 with an infrared absorption efficiency of α1 and a thermopile internal resistance in series, and the thermopile II in the differential structure thermopile can be equivalent to the thermoelectric potential V generated by the self-heating of ASIC. ASIC The circuit is composed of a thermoelectromotive force V2 with an infrared absorption efficiency of α2 and a thermopile internal resistance R in series. After the ASIC completes the subtraction operation of the total output thermoelectromotive force of thermopile I and thermopile II, the net output thermoelectromotive force can be equivalent to a voltage source composed of a thermoelectromotive force V3 with an infrared absorption efficiency of α1-α2 and a thermopile internal resistance R in series, which has nothing to do with the self-heating of the chip, thereby completing the influence of the self-heating of the ASIC and completing the decoupling of the MEMS thermopile and the ASIC circuit.
[0024] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.
Claims
1. A CMOS-MEMS monolithic integrated thermopile infrared detector with a thermal decoupling structure, characterized in that: It includes a MEMS thermopile, an ASIC circuit and a thermal decoupling structure; the MEMS thermopile includes a thermopile I and a thermopile II, and the infrared absorption efficiency of the thermopile I and the thermopile II are different; the thermal decoupling structure includes a thermal insulation cavity located at the back of the MEMS thermopile, a heat dissipation microchannel located under the ASIC circuit and a thermal isolation groove located between the MEMS thermopile and the ASIC circuit.
2. The CMOS-MEMS monolithic integrated thermopile infrared detector with thermal decoupling structure according to claim 1, characterized in that: The MEMS thermopile is a MEMS thermopile chip formed on the front side of a single crystal silicon wafer by a CMOS process. The main body presents a differential structure and is composed of a thermopile I and a thermopile II with highly symmetrical structures.
3. The CMOS-MEMS monolithic integrated thermopile infrared detector with thermal decoupling structure according to claim 2, characterized in that: The thermopile I and the thermopile II are both formed by connecting thermocouples in series after being patterned by photolithography, and the polysilicon layer and the metal layer of the thermocouples are connected through tungsten through holes.
4. The CMOS-MEMS monolithic integrated thermopile infrared detector with thermal decoupling structure according to claim 2, characterized in that: The thermopile I and the thermopile II are on the same horizontal plane and arranged vertically. The thermopile I uses the silicon nitride passivation layer in the CMOS process as the infrared absorption layer, and the thermopile II uses a thin film with high infrared reflectivity as the infrared absorption layer.
5. The CMOS-MEMS monolithic integrated thermopile infrared detector with thermal decoupling structure according to claim 1, characterized in that: The ASIC circuit is prepared on a single crystal silicon wafer using a standard CMOS process, and is composed of a differential operational amplifier module, an analog-to-digital converter, an on-chip temperature sensor, a reference voltage module, and a microcontroller module. The module with high power consumption is placed in the center, and the modules with low power consumption are evenly distributed at both ends.
6. The CMOS-MEMS monolithic integrated thermopile infrared detector with thermal decoupling structure according to claim 4, characterized in that: The differential operational amplifier module is used to make a difference between the output thermoelectric potentials of thermopile I and thermoelectric pile II and to amplify them appropriately to eliminate the thermoelectric potential caused by the self-heating effect of ASIC; the analog-to-digital converter is used to convert the analog output thermoelectric potential into a digital signal and transmit it to the microcontroller MCU module for subsequent processing; the on-chip temperature sensor is used to monitor the cold end temperature of the thermopile.
7. The CMOS-MEMS monolithic integrated thermopile infrared detector with thermal decoupling structure according to claim 1, characterized in that: The thermopile I and the thermopile II share the same heat-insulating cavity.