Environmentally robust multi-integrated MEMS tactile sensor and method of fabrication thereof

Abstract

The application provides an anti-interference multi-integrated MEMS tactile sensor and a manufacturing method thereof. The application comprises a substrate which is a wafer made of silicon; a temperature sensor located on the substrate; a pressure sensor located on the substrate; a thermal infrared detector located on the substrate; and a heat conduction sensor located on the substrate, wherein the heat conduction sensor comprises, from bottom to top, a lower silicon substrate, an upper silicon substrate, an electrically insulating layer and a concentric chromium / platinum film layer. The concentric chromium / platinum film layer in the application adopts a concentric square ring structure, and a certain space exists between the inner ring and the outer ring. This design can eliminate the temperature drift and bending / tension strain in the heat conduction sensor, and can also avoid the thermal interference of the inner ring on the outer ring. The application can realize multi-dimensional measurement of a contacted object, and can simultaneously sense the heat conductivity, contact pressure, external temperature and thermal radiation of the contacted object under the premise of low cost and small size.

Description

TECHNICAL FIELD

[0001] The present application provides an anti-interference multi-integrated MEMS tactile sensor and a manufacturing method thereof, which can realize the functions of contact temperature measurement, infrared temperature measurement, thermal conductivity measurement and pressure measurement. BACKGROUND

[0002] Multi-modal tactile sensing is very important for realizing environmental judgment, threat identification and fine motor tasks, and delicate and accurate tactile ability is also very important for complex applications of robots and prostheses. Multi-integrated tactile sensors can enable robots to accurately, quickly and safely interact with their surroundings. Many researchers have previously proposed various tactile sensors based on piezoresistance, capacitance, triboelectricity, electret, magnetism, etc., and have developed multi-sensory e-skins by directly integrating different sensors into a sensing network or array with a stacked or planar structure, or using customized advanced materials and microstructures sensitive to physical stimuli. Although significant progress has been made in the development of tactile sensors, they still require complex structures and manufacturing solutions, and often have the problem of mutual interference when simultaneously sensing multiple stimuli.

[0003] Single-chip integrated composite sensors are an ideal choice for the next generation of sensing nodes, which will have the advantages of smaller size, lower power consumption and lower assembly cost by integrating various sensing elements with micro-electro-mechanical system (MEMS) technology on a single chip. By utilizing the manufacturing technology of modern IC / MEMS foundries, the uniformity of the sensor can be maximized and the cost of the product can be minimized.

[0004] Tactile sensing is also useful in robotics for object recognition or grasping tasks. Existing tactile object recognition is mainly based on pressure / force sensing. However, for complex object recognition, pressure / force sensing alone is not enough. Substances with similar mechanical properties cannot be distinguished by contact pressure alone, and based on this, the different thermal conductivities of different materials can be used to combine thermal characteristics with the mechanical characteristics of the object to improve recognition accuracy. Therefore, the present application provides a multi-integrated MEMS tactile sensor with anti-interference capability, which is of great significance for industrial applications and the design of mechanical hands. SUMMARY

[0005] The present application aims to provide an anti-environmental interference multi-integrated MEMS tactile sensor that can simultaneously realize the functions of pressure sensing, temperature sensing, thermal conductivity measurement and infrared sensing.

[0006] An anti-environmental interference multi-integrated MEMS tactile sensor, comprising:

[0007] a substrate made of a silicon wafer;

[0008] a temperature sensor on the substrate, the temperature sensor comprising, from bottom to top, an electrically insulating layer and a thermistor, the electrically insulating layer being in direct contact with the thermistor;

[0009] a pressure sensor on the substrate, the pressure sensor comprising, from bottom to top, an electrically insulating layer, a pressure chamber and a pressure sensitive resistor, the electrically insulating layer being in direct contact with the pressure chamber and extending to the upper surface of the pressure chamber, the pressure sensitive resistor being on the upper surface of the pressure chamber and in direct contact with the extended electrically insulating layer;

[0010] a pyroelectric infrared detector on the substrate, the pyroelectric infrared detector comprising, from bottom to top, an electrically insulating layer, a concave cavity, a central boss, a silicon nitride absorbing layer and a thermocouple, the concave cavity being on the substrate, the central boss being in the center of the concave cavity, the silicon nitride absorbing layer being on the substrate and horizontally extending to the upper surface of the central boss, the silicon nitride absorbing layer being suspended directly above the concave cavity, the thermocouple being on the upper surface of the silicon nitride absorbing layer, the electrically insulating layer being in direct contact with the silicon nitride absorbing layer;

[0011] a thermal conductive sensor on the substrate, the thermal conductive sensor comprising, from bottom to top, a lower silicon substrate, an upper silicon substrate, an electrically insulating layer and a concentric chromium / platinum thin film layer, the lower silicon substrate being on the substrate, the upper silicon substrate comprising, from bottom to top, a bottom silicon layer, a porous material layer, a PDMS layer and a top silicon layer, the bottom silicon layer being on the substrate, the porous material layer being on the bottom silicon layer, the PDMS layer being on the porous material layer, the top silicon layer being on the PDMS layer, the concentric chromium / platinum thin film layer being on the bottom silicon layer and the top silicon layer respectively, the electrically insulating layer being on the lower silicon substrate and horizontally extending to the upper silicon substrate, the electrically insulating layer being suspended directly above the substrate, the electrically insulating layer being in direct contact with the concentric chromium / platinum thin film layer.

[0012] Further, the number of the electrically insulating layers in the temperature sensor is 2, which are respectively below and in direct contact with the thermistor, the electrically insulating layers and the thermistor are both on the substrate.

[0013] Further, the pressure chamber in the pressure sensor is in the overall cuboid structure, the inside of the pressure chamber is vacuum, the number of the pressure sensitive resistors is 4, which are all on the upper surface of the outside of the pressure chamber and spaced apart at a certain distance, the number of the electrically insulating layers is also 4 and they are not in contact with each other, which are all on the substrate and extend to the upper surface of the pressure chamber, the electrically insulating layers are in direct contact with the pressure chamber and the pressure sensitive resistors.

[0014] Further, the concave cavity in the pyroelectric infrared detector is etched on the substrate, the center boss is located in the center of the concave cavity, the height of the center boss is equal to the depth of the concave cavity, and the 15 silicon nitride absorption layers are distributed as follows: 4 on the upper left, 4 on the upper right, 4 on the lower left, and 3 on the lower right. The silicon nitride absorption layers are located on the substrate and extend horizontally to the upper surface of the center boss, and the silicon nitride absorption layers are suspended above the concave cavity. The number of thermocouples is also 15, which are respectively distributed on the upper surfaces of the 15 silicon nitride absorption layers. The number of electrically insulating layers is 2, which are located on the lower right of the substrate, parallel to the remaining 3 silicon nitride absorption layers in the same direction, and extend horizontally to the upper surface of the center boss. The electrically insulating layer is suspended above the concave cavity.

[0015] Further, the upper silicon substrate and the lower silicon substrate in the heat-conducting sensor have equal height and width, the lower silicon substrate is only silicon, and the upper silicon substrate is composed of a bottom silicon layer, a porous material layer, a PDMS layer, and a top silicon layer from bottom to top. The concentric chromium / platinum thin film layer is located on the bottom silicon layer and the top silicon layer, respectively. The concentric chromium / platinum thin film layer is square. The number of electrically insulating layers is 4, which are respectively located on the lower silicon substrate and extend horizontally to the upper surface of the upper silicon substrate. The electrically insulating layer directly contacts the four ends of the concentric chromium / platinum thin film layer.

[0016] A method for manufacturing an environmentally resistant multi-integrated MEMS tactile sensor, comprising the following steps:

[0017] A 4-inch silicon wafer is manufactured, and the substrate is doped by boron iron injection. Then the substrate is annealed in oxygen, and kept at 1100°C for 65 minutes to activate the impurity doping and obtain a 0.5 μm thick thermal oxide layer at the same time. Next, a 0.5 μm thick low-stress silicon nitride film is deposited by low-pressure chemical vapor deposition. The manufactured silicon dioxide / silicon nitride film serves as an electrically insulating layer for the pressure sensor and the temperature sensor. In the pyroelectric infrared detector part, the silicon dioxide / silicon nitride film is removed by reactive ion etching to reduce the thickness of the final absorption film.

[0018] A 2 μm thick low-temperature oxide and a 0.25 μm thick phosphosilicate glass are sequentially deposited and patterned by low-pressure chemical vapor deposition. The phosphosilicate glass / low-temperature oxide layer is used as a sacrificial structure for the pressure sensor. The low-temperature oxide defines the gap between the functional layer and the substrate. The phosphosilicate glass layer covering the low-temperature oxide can accelerate the lateral etching speed, where the content of phosphorus determines the etching speed. The lateral release hole is composed of phosphosilicate glass, which facilitates sealing later.

[0019] A 1.2 μm thick LS-silicon nitride is deposited by low pressure chemical vapor deposition at 875 °C. This multifunctional layer serves as the pressure chamber in the pressure sensor and as the absorbing membrane in the pyroelectric infrared detector. By adjusting the flow rate of the gases, the silicon-rich silicon nitride is tuned to achieve a low residual tensile stress of about 100 MPa, as measured by a laser scanning profilometer. A 0.8 μm thick fine-grained polysilicon is then deposited by low pressure chemical vapor deposition at 620 °C and is followed by a B+ implant. The polysilicon layer is patterned to form the piezoresistors, thermocouples and thermistors. Next, the 1.2 μm thick LS-silicon nitride film is patterned by reactive ion etching to open the release holes for the sacrificial layer etch.

[0020] The sacrificial low temperature oxide layer is removed with 40% hydrofluoric acid for 8-10 minutes. The etching process can be monitored by a microscope through the transparent silicon nitride membrane. A 1.4 μm thick tetraethyl orthosilicate is deposited by low pressure chemical vapor deposition and is patterned by a buffer oxide etch to seal the release holes.

[0021] The polysilicon resistors with a sheet resistance of 100 Ω / sq are annealed in an oxygen ambient at 1,100 °C for 1 hour to obtain a uniform ion distribution. At the same time, a 0.4 μm thick thermal oxide is grown outside the polysilicon and a 0.2 μm thick LS-silicon nitride is deposited by low pressure chemical vapor deposition. Next, contact holes are opened by reactive ion etching and a 0.6 μm thick aluminum layer is sputtered and patterned to interconnect the thermocouple part of the pyroelectric infrared detector. At this point, the processing of the pressure sensor and temperature sensor is complete.

[0022] The release slots of the pyroelectric infrared detector are opened and bulk micromachining is used to remove the silicon substrate under the pyroelectric infrared detector absorbing membrane and the thermocouple to achieve thermal isolation. The silicon is then etched by a xenon difluoride isotropic dry etch process with xenon difluoride at 2 torr and nitrogen at 60 torr for 20 s per cycle for a total of 800 cycles to achieve an etch depth of about 50 μm. At this point, the fabrication of the pyroelectric infrared detector is complete.

[0023] Finally, a lid wafer with a reactive ion etch processing cavity is fabricated and coated with 2 μm thick benzocyclobutene and bonded to the lid wafer to protect the pyroelectric infrared detector during subsequent dicing. The piezoresistors and thermistors are placed outside the lid wafer.

[0024] The concentric chromium / platinum thin film layer of the heat conduction sensor is prepared by spin coating 30 μm photoresist on a silicon plate, obtaining a pattern by photoetching and developing, sputtering 30 nm thick chromium as an adhesion layer, and then sputtering 150 nm thick platinum as a adhesion layer heat sensitive layer. The patterned substrate is immersed in acetone for 2 hours to dissolve the photoresist, then washed with anhydrous ethanol and deionized water, and finally a 4 μm thick parylene film is deposited on the patterned substrate as a protective layer.

[0025] The porous material of the heat conduction sensor is made of PDMS, citric acid monohydrate particles and silver nanoparticles. In the material preparation, the volume ratio of PDMS to citric acid monohydrate is 1:3, the volume ratio of PDMS to crosslinking agent is 10:1, and the volume ratio of silver nanoparticles is 2%. After the mixture is stirred for 10 minutes, it is poured into a PMMA mold and cured at 75°C for 2 hours. After demolding, the material is immersed in ethanol for 24 hours to dissolve the citric acid monohydrate and form pores, then washed with deionized water, and finally dried at 70°C for 1 hour. Finally, the sensing layer is adhered to the upper surface of the prepared PDMS layer and the lower surface of the porous material, and the heat conduction sensor is completed.

[0026] Advantages of the present application:

[0027] 1. The structure design of the heat conduction sensor part realizes innovation. The concentric chromium / platinum thin film layer on the bottom silicon layer and the top silicon layer of the heat conduction sensor adopts a concentric square ring structure, and there is a certain space between the inner ring and the outer ring. This design can not only eliminate the temperature drift and bending / tension strain in the heat conduction sensor, but also avoid the thermal interference of the inner ring to the outer ring. In traditional integrated sensors, the overall structure of the heat conduction sensor is relatively small, and the design of the inner ring and the outer ring of the concentric chromium / platinum thin film layer is relatively compact. Therefore, when the heat conduction sensor works, the heat generated by the inner ring may interfere with the temperature sensor and the thermoelectric infrared detector, and may also interfere with the outer ring, thereby affecting the sensing performance. Compared with traditional heat conduction sensors, the structure design of the heat conduction sensor in the multi-integrated MEMS tactile sensor of the present application has a larger space between the inner ring and the outer ring of the concentric chromium / platinum thin film layer, so it can obtain higher sensitivity and reduce the thermal interference of the inner ring to the outer ring. The inner ring is smaller and the outer ring is larger, so the thermal interference of the inner ring to other parts of the sensor when it generates heat can be minimized, thereby greatly improving the reliability of the heat conduction sensor. The PDMS layer and the flexible porous material layer are provided between the top silicon layer and the bottom silicon layer of the heat conduction sensor. When the porous material layer is deformed under external pressure, it can increase its own thermal conductivity, and also enhance the heat conduction from the inner ring of the concentric chromium / platinum thin film layer on the bottom silicon layer to the surrounding of the bottom silicon layer.

[0028] 2. The heat conduction sensor in the multi-integrated MEMS tactile sensor can change the sensitivity required by the heat conduction sensor by changing the size of the space between the inner ring and the outer ring in the concentric chromium / platinum thin film layer. When the space between the inner ring and the outer ring is reduced, the sensitivity of the heat conduction sensor will decrease; when the space between the inner ring and the outer ring is increased, the sensitivity of the heat conduction sensor will increase. If it is desired to reduce the overall size of the heat conduction sensor in actual application without losing its high sensitivity, the size of the inner ring and the outer ring of the concentric chromium / platinum thin film layer in the top silicon layer and the bottom silicon layer can be reduced.

[0029] 3. As an integrated sensor with four measurement functions, the MEMS multi-integrated tactile sensor can measure multiple dimensions of the contacted object and simultaneously sense the heat conductivity, contact pressure, external temperature and thermal radiation of the contacted object under the premise of low cost and small size. Since the selected manufacturing materials have excellent mechanical and electrical properties, the present application can be used in many situations, such as industrial environments, buildings, transportation facilities, and robot hands.

[0030] 4. The multifunctional silicon nitride / polysilicon / aluminum layer can well realize multiple sensing functions. In the manufacturing process, the sensor manufacturing process of each part can be performed in parallel, and different sensing structures can be designed and integrated into a single chip by sharing manufacturing steps and compatible materials. More importantly, the proposed design / manufacturing module concept can realize a low-cost single-chip integrated "function library", which will significantly save the design / manufacturing / encapsulation cost of multifunctional sensor network nodes. Such integrated sensors not only can monitor various objects or parameters, but also can obtain better sensing characteristics through information fusion. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a structural top view of the present application.

[0032] Figure 2 is a three-dimensional schematic view of the structure of the present application.

[0033] Figure 3 is a right view of the structure of the present application.

[0034] Figure 4 is a top view of the temperature sensor in the present application.

[0035] Figure 5 is a top view of the pressure sensor in the present application.

[0036] Figure 6 is a top view of the pyroelectric infrared detector in the present application.

[0037] Figure 7 is a top view of the heat conduction sensor in the present application.

[0038] Figure 8 is the right view of the heat conduction sensor part in the present application

[0039] Figure 9 is the process flow chart of the temperature sensor in the present application.

[0040] Figure 10 is the process flow chart of the pressure sensor in the present application.

[0041] Figure 11 is the process flow chart of the pyroelectric infrared detector in the present application.

[0042] Figure 12 is the process flow chart of the heat conduction sensor in the present application. DETAILED DESCRIPTION

[0043] In order to better understand the present application, it will be specifically described below in combination with the drawings.

[0044] The present application provides an integrated tactile sensor which can realize temperature, heat conductivity, infrared and pressure measurement, comprising a substrate, a temperature sensor, a pressure sensor, a pyroelectric infrared detector and a heat conduction sensor.

[0045] The multi-integrated MEMS tactile sensor has the following functions: the pressure sensor monitors absolute pressure; the heat conduction sensor judges the heat conductivity of the contacted object; the pyroelectric infrared detector monitors the change of thermal radiation from the environment; and the temperature sensor monitors the reference temperature of the environment. The multi-integrated sensor can calibrate the temperature drift of the equipment, and can be used in the applications of buildings, traffic facilities or machine hands, and can be used for environmental monitoring, danger warning and safety management.

[0046] The multi-integrated MEMS tactile sensor has the following features: the pressure sensor has a sealed pressure chamber on the substrate, the outer diaphragm of the pressure chamber is made of silicon nitride, and the piezoresistor made of polysilicon is made on the upper surface of the outer diaphragm; the heat conduction sensor part is made by directly depositing on the substrate, and the concentric chromium / platinum film covered by the poly-p-xylylene encapsulation film is used as the protective layer; the pyroelectric infrared detector uses the suspended silicon nitride absorption layer above the concave cavity and the thermocouple made of polysilicon / aluminum; and the thermistor is made of polysilicon strip.

[0047] The multi-integrated MEMS tactile sensor, the top silicon layer and the bottom silicon layer of the thermal conductive sensor are two completely same sensing layers, each of which is composed of a concentric chromium / platinum thin film layer and is directly deposited on the bottom and top silicon layers and is covered by a parylene encapsulation. There is a porous material layer and a PDMS layer between the top silicon layer and the bottom silicon layer, the porous material layer is arranged above the bottom silicon layer, the PDMS layer is arranged above the porous material layer, and the top silicon layer is arranged above the PDMS layer. The concentric square ring design of the inner ring and the outer ring in the concentric chromium / platinum thin film layer eliminates the temperature drift and bending / tension strain in the sensor. The inner ring in the concentric chromium / platinum thin film layer has a relatively lower resistance than the outer ring, and under the same applied voltage, the inner ring with lower resistance bears larger electric power and is heated to a predetermined higher temperature, thereby playing a role of 'hot film'; the outer ring with larger resistance bears low Joule heat and plays a role of 'cold film'. The inner ring of the concentric chromium / platinum thin film layer on the top silicon layer and the bottom silicon layer generates a local thermal field around it, and when an object contacts and presses the entire sensor, the object contacts the top silicon layer, and the conductive heat from the inner ring of the concentric chromium / platinum thin film layer on the top silicon layer to the surrounding thereof changes with the thermal conductivity of the object.

[0048] The multi-integrated MEMS tactile sensor, the inner ring of the concentric chromium / platinum thin film layer on the top silicon layer of the thermal conductive sensor responds to the thermal conductivity of the contacted object, and the thermal conductivity of the object is detected through the inner ring of the concentric chromium / platinum thin film layer on the top silicon layer of the sensor. At the same time, the pressure applied on the entire sensor causes the elastic deformation of the porous material. The deformation of the porous material can increase the thermal conductivity and enhance the heat transfer from the inner ring of the concentric chromium / platinum thin film layer on the bottom silicon layer to the surrounding thereof. The outer ring of the concentric chromium / platinum thin film layer on the top silicon layer and the bottom silicon layer can also be used as a local temperature sensor, the outer ring of the concentric chromium / platinum thin film layer on the top silicon layer is used to detect the temperature of the object, and the outer ring of the concentric chromium / platinum thin film layer on the bottom silicon layer is used to detect the ambient temperature. For the bottom silicon layer and the top silicon layer, there is a certain space between the inner ring and the outer ring of the concentric chromium / platinum thin film layer, which avoids the thermal interference of the inner ring on the outer ring and can change the sensitivity of the thermal conductive sensor by changing the size of the space between the inner ring and the outer ring. When the space between the inner ring and the outer ring decreases, the sensitivity of the thermal conductive sensor decreases; when the space between the inner ring and the outer ring increases, the sensitivity of the thermal conductive sensor increases.

[0049] The multi-integrated MEMS tactile sensor has a pressure sensor structure based on a vacuum pressure chamber, four piezoresistors are arranged on the upper surface of an outer diaphragm outside the pressure chamber to form a Wheatstone bridge, when pressure is applied to the outer diaphragm of the pressure chamber, the outer diaphragm deflects and causes stress distribution, therefore, a rectangular diaphragm with a high length-width ratio is designed, and the stress distribution near the center of the outer diaphragm is quasi-one-dimensional, wherein the stress in the width direction is much larger than that in the length direction. Meanwhile, four piezoresistors are designed, and the piezoresistors have a zigzag shape, and the longitudinal parts of the piezoresistors are arranged in the high stress area in the width direction to improve the sensitivity.

[0050] The multi-integrated MEMS tactile sensor has a thermal infrared detector composed of a silicon nitride absorption layer and a series of thermocouples. The main part of the silicon nitride absorption film and the thermocouples are suspended on a substrate with a deep etched cavity to ensure good thermal insulation. One end of the thermocouple close to the substrate is called the cold end, and the other end far from the substrate is called the hot end. The thermocouple absorbs high-temperature infrared radiation from the detected object, and the silicon nitride absorption layer raises the temperature of the hot end. At this time, the temperature difference between the hot end and the cold end will cause a corresponding voltage output.

[0051] The multi-integrated MEMS tactile sensor has a substrate made of boron-doped silicon, and the thermistors and piezoresistors are made of polysilicon. The thermocouples in the thermal infrared detector are made of polysilicon / aluminum layers, the absorption film is made of silicon nitride, and the top and bottom silicon layers in the thermal conductivity sensor have concentric chromium / platinum films covered by a parylene encapsulation film.

[0052] The application also provides a manufacturing method of the four-integrated tactile sensor capable of measuring temperature, thermal conductivity, pressure and infrared, which comprises the following steps:

[0053] A 4-inch silicon wafer is manufactured, and the substrate is doped by boron iron injection. Then the substrate is annealed in oxygen at 1100 DEG C for 65 minutes to activate the impurity doping and obtain a 0.5 mu m thick thermal oxide layer. Next, a 0.5 mu m thick low-stress silicon nitride film is deposited by low-pressure chemical vapor deposition. The manufactured silicon dioxide / silicon nitride film acts as an electrical insulation layer of the pressure sensor and the temperature sensor. In the thermal infrared detector part, the silicon dioxide / silicon nitride film is removed by reactive ion etching to reduce the thickness of the final absorption film.

[0054] A 2 μm thick low temperature oxide and a 0.25 μm thick phosphosilicate glass are sequentially deposited and patterned by low pressure chemical vapor deposition. The phosphosilicate glass / low temperature oxide layer is used as a sacrificial structure for the pressure sensor. The low temperature oxide defines the gap between the functional layer and the substrate. The phosphosilicate glass layer over the low temperature oxide can speed up the lateral etch rate, where the phosphorous content determines the etch rate. The lateral release holes are composed of phosphosilicate glass for later sealing.

[0055] A 1.2 μm thick LS-silicon nitride is deposited at 875 °C by low pressure chemical vapor deposition. This multifunctional layer is used as a pressure chamber in the pressure sensor, and as an absorption film in the pyroelectric infrared detector. By adjusting the flow rate of the gases, the silicon-rich silicon nitride is adjusted to have a low residual tensile stress of about 100 MPa, measured by a laser scanning profilometer. A 0.8 μm thick fine-grained polysilicon is then deposited at 620 °C by low pressure chemical vapor deposition, followed by a B+ implant. The polysilicon layer is patterned to form the piezoresistors, thermocouples, and thermistors. Next, the 1.2 μm thick LS-silicon nitride film is patterned by reactive ion etching to open the release holes for the sacrificial layer etching.

[0056] The sacrificial low temperature oxide layer is removed with 40% hydrofluoric acid for 8-10 minutes, and the etching process can be checked under a microscope through the transparent silicon nitride membrane. A 1.4 μm thick tetraethyl orthosilicate is deposited by low pressure chemical vapor deposition and patterned by a buffer oxide etch to seal the release holes.

[0057] The polysilicon resistors with a sheet resistance of 100 Ω / sq are annealed in an oxygen ambient at 1,100 °C for 1 hour to obtain a uniform ion distribution. At the same time, a 0.4 μm thick thermal oxide is obtained outside the polysilicon, followed by a 0.2 μm thick LS-silicon nitride deposited by low pressure chemical vapor deposition. Next, the contact holes are opened by reactive ion etching, and a 0.6 μm thick aluminum layer is sputtered and patterned for interconnecting the thermocouple part of the pyroelectric infrared detector. At this point, the processing of the pressure sensor and temperature sensor is completed.

[0058] The release slots of the pyroelectric infrared detector are opened, and bulk micromachining is used to remove the silicon substrate under the pyroelectric infrared detector absorption film and the thermocouple to a certain depth to achieve thermal isolation, followed by a xenon difluoride isotropic dry etching process, where the xenon difluoride is 2 torr, the nitrogen is 60 torr, each cycle is set to 20 s, a total of 800 cycles are performed, and the etching depth is about 50 μm. At this point, the fabrication of the pyroelectric infrared detector is completed.

[0059] Finally, a cover wafer with a reactive ion etching chamber is fabricated, coated with a 2μm thick layer of benzocyclobutene and bonded to the cover wafer to protect the thermoelectric infrared detector during subsequent dicing. The varistor and thermistor are placed outside the cover wafer.

[0060] The concentric chromium / platinum thin film layer for the thermally conductive sensor can be fabricated by first spin-coating a 30 μm photoresist onto a silicon substrate, obtaining a pattern through photolithography and development, sputtering a 30 nm thick chromium layer as an adhesion layer, and then sputtering a 150 nm thick platinum layer as the adhesion and thermal layer. The patterned substrate is then immersed in acetone for 2 hours to dissolve the photoresist, followed by washing with anhydrous ethanol and deionized water. Finally, a 4 μm thick parylene film is deposited on the patterned substrate as a protective layer.

[0061] The porous material of the thermally conductive sensor is made of PDMS, citric acid monohydrate particles, and silver nanoparticles. In the material fabrication process, the volume ratio of PDMS to citric acid monohydrate is set to 1:3, the volume ratio of PDMS to crosslinking agent is 10:1, and the silver nanoparticles account for 2% of the volume. After thoroughly stirring the mixture for 10 minutes, it is poured into a PMMA mold and cured at 75°C for 2 hours. After demolding, the material is immersed in ethanol for 24 hours to dissolve the citric acid monohydrate and form pores. It is then washed with deionized water and finally dried at 70°C for 1 hour. Finally, the sensing layer is adhered to the upper surface of the fabricated PDMS layer and the lower surface of the porous material, thus completing the fabrication of the thermally conductive sensor.

[0062] Example:

[0063] like Figure 1 The diagram shows a top view of a multi-integrated MEMS tactile sensor, which includes a temperature sensor 8a, a pressure sensor 8b, a thermoelectric infrared detector 8c, and a thermal conductivity sensor 8d.

[0064] like Figure 2 As shown, a three-dimensional schematic diagram of a multi-integrated MEMS tactile sensor is presented, including a temperature sensor 8a, a pressure sensor 8b, a thermoelectric infrared detector 8c, and a thermal conductivity sensor 8d.

[0065] like Figure 3 As shown, a right view of a multi-integrated MEMS tactile sensor is shown, where 1a is a substrate made of silicon.

[0066] like Figure 4 As shown, a temperature sensor portion of a multi-integrated MEMS tactile sensor includes a thermistor 5a made of polycrystalline silicon and electrically insulating layers 6a and 6b made of silicon nitride.

[0067] like Figure 5As shown, in a multi-integrated MEMS tactile sensor, the pressure sensor part consists of 5b, 5c, 5d, and 5e, which are piezoresistors made of polycrystalline silicon; 6c, 6d, 6e, 6f, 6i, 6j, 6k, 6l, 6m, 6n, 6o, and 6p, which are electrically insulating layers; and 6q, which is a pressure chamber made of silicon nitride.

[0068] like Figure 6 As shown, in a multi-integrated MEMS tactile sensor, the thermoelectric infrared detector part consists of 5f, 5g, 5h, 5i, 5j, 5k, 5l, 5m, 5n, 5o, 5p, 5q, 5r, 5s, and 5t, which are thermocouples made of polycrystalline silicon; and 7a, 7b, 7c, 7d, 7e, 7f, 7g, 7h, 7i, 7j, 6g, 6h, 6r, 6s, 6t, 6u, and 6v, which are electrically insulating layers made of silicon nitride.

[0069] like Figure 7 As shown, in a multi-integrated MEMS tactile sensor, the thermally conductive sensor part includes an upper silicon substrate and a lower silicon substrate, respectively. 4a and 4b are concentric chromium / platinum thin film layers covered by a parylene encapsulation film protective layer. 6w, 6x, 6y, and 6z are electrically insulating layers made of silicon nitride.

[0070] like Figure 8 As shown, this is a right view of the thermally conductive sensor portion in a multi-integrated MEMS tactile sensor. 1b is the upper silicon substrate, 4b is a concentric chromium / platinum thin film layer covered by a parylene encapsulation film protective layer, 9 is a PDMS layer, and 10 is a porous material layer.

[0071] The working principle of this invention is:

[0072] 5a, 6a, and 6b form a temperature sensor. When stimulated by external touch, thermistor 5a changes its resistance value according to the temperature of the signal source, thereby outputting a corresponding voltage value. The sensor circuit can convert the output voltage into a displayable temperature value.

[0073] The pressure sensor is composed of 6c, 6d, 6e, 6f, 6i, 6j, 6k, 6l, 6m, 6n, 6o, 6p, 6q and 5b, 5c, 5d, 5e. When stimulated by external touch signals, the pressure-sensitive resistors 5b, 5c, 5d, 5e will change their resistance values ​​according to the pressure of the signal source, thereby outputting a corresponding voltage value. The sensor circuit can convert the output voltage into a displayable pressure value.

[0074] 7a, 7b, 7c, 7d, 7e, 7f, 7g, 7h, 7i, 7j, 6g, 6h, 6r, 6s, 6t, 6u, 6v, 5f, 5g, 5h, 5i, 5j, 5k, 5l, 5m, 5n, 5o, 5p, 5q, 5r, 5s, 5t constitute a thermoelectric infrared detector, when receiving external touch stimulus signal, the heat field released by the signal source will affect the thermoelectric infrared detector, the output voltage of the hot end and the cold end in the thermocouple will output corresponding values according to the thermal radiation, and the sensor circuit can convert the output voltage into a displayable thermal radiation value.

[0075] 1b, 1c, 4a, 4b, 6w, 6x, 6y, 6z constitute a thermal conductive sensor, when receiving external touch stimulus signal, the material type of the signal source will affect the concentric chromium / platinum film layer on the top silicon layer, the concentric chromium / platinum film layers 4a and 4b on the upper silicon substrate 1b work together to output corresponding voltage, 4a constitutes an outer ring, has a larger resistance value, bears less Joule heat, and becomes a "cold film"; 4b constitutes an inner ring, has a smaller resistance value, and becomes a "hot film", the inner ring and the outer ring work together to output voltage, and the output voltage is calculated to become a corresponding thermal conductivity, and the attribute of the material can be judged according to the thermal conductivity value.

[0076] In summary, the multi-integrated MEMS tactile sensor can perceive four-dimensional stimulus signals from the outside world, and can simultaneously measure the temperature, applied pressure, thermal radiation and thermal conductivity of the stimulus signal. The existing tactile object recognition is mainly based on pressure sensing, but for complex object recognition, the multi-dimensional integrated tactile sensor in the present application can utilize the fact that different materials have different thermal conductivities, combine thermal characteristics with mechanical characteristics of the object, and improve the recognition accuracy. Even if the substances have similar mechanical characteristics, the object recognition can also be realized, and in addition, the multi-dimensional tactile perception is also useful for object recognition or grasping tasks in robot technology. Therefore, the present application provides a multi-integrated MEMS tactile sensor, which is of great significance for industrial applications and mechanical hand design.

[0077] The present example relates to a manufacturing method of the multi-integrated MEMS tactile sensor, which is described as follows in combination with the process flow.

[0078] Figure 9 For Figure 1 The process flow chart of the temperature sensor part, the same filling pattern represents the same material.

[0079] (a) Prepare a 4-inch silicon wafer doped with boron iron as a substrate, and form a silicon dioxide / nitride film on the surface as an electrical insulation layer.

[0080] (b) Deposit 0.8 μm thick polysilicon at 620 ℃ by low pressure chemical vapor deposition and perform boron ion implantation, and pattern the same to form a thermistor.

[0081] (c) Sputter and pattern 0.6 μm of aluminum to complete the temperature sensor.

[0082] Figure 10 For Figure 1 Process flow chart for the medium pressure sensor portion. The same fill pattern indicates the same material.

[0083] (a) Fabricate a silicon dioxide / silicon nitride film on the silicon substrate as the electrical isolation layer for the pressure sensor.

[0084] (b) Deposit 2 μm of low temperature oxide and 0.25 μm of phosphosilicate glass by chemical vapor deposition and pattern sequentially. The low temperature oxide layer and the phosphosilicate glass are used as sacrificial structures.

[0085] (c) Deposit 1.2 μm of silicon nitride by low pressure chemical vapor deposition at 875 °C to form the pressure chamber. Deposit 0.8 μm of polysilicon at 620 °C and implant boron ions. Pattern to form the piezoresistor. Design and etch the release holes.

[0086] (d) Remove the low temperature oxide sacrificial layer with 40% hydrofluoric acid. Deposit 1.4 μm of tetraethyl orthosilicate and pattern to seal the release holes.

[0087] (e) Anneal in oxygen at 1100 °C for one hour. Deposit 0.2 μm of silicon nitride. Open the contact holes by reactive ion etching. Sputter and pattern aluminum to complete the pressure sensor.

[0088] Figure 11 For Figure 1 Process flow chart for the medium thermopile infrared detector portion. The same fill pattern indicates the same material.

[0089] (a) Fabricate a silicon dioxide / silicon nitride film on the silicon substrate. Remove a portion of the film to reduce the thickness by reactive ion etching.

[0090] (b) Deposit 1.2 μm of silicon nitride by chemical vapor deposition at 875 °C to be used as the absorber film in the infrared detector.

[0091] (c) Sputter and pattern 0.6 μm of aluminum to be used as the electrical interconnect and the thermocouple portion.

[0092] (d) Open the release slots in the silicon nitride layer of the thermopile infrared detector.

[0093] (e) Remove the substrate under the absorber film and the thermocouple by bulk micromachining to achieve thermal isolation. Etch the substrate approximately 50 μm deep with xenon difluoride to complete the thermopile infrared detector.

[0094] Figure 12 For Figure 1 Process flow chart of fabricating the thermal sensor part. The same fill pattern represents the same material.

[0095] A bulk silicon thin film is fabricated on a substrate; a square ring pattern is obtained by photolithography and development; 0.03 μm thick chromium is sputtered as an adhesion layer, and then 0.15 μm thick platinum is sputtered as an adhesion layer and a thermal sensitive layer; the patterned substrate is immersed in acetone for 2 hours to dissolve the photoresist, and then washed with anhydrous ethanol and deionized water, and then a 4 μm thick parylene film is deposited as a protective layer, thus the bottom silicon layer and the concentric chromium / platinum thin film layer are completed, and another piece is fabricated as the top silicon layer and the concentric chromium / platinum thin film layer by using the same process flow as described above; the porous material and the PDMS are sequentially placed on the bottom silicon layer, and finally the fabricated top silicon layer is placed on the PDMS layer, thus the thermal sensor is completed.

Claims

1. A method for manufacturing an environmentally robust multi-integrated MEMS tactile sensor, the multi-integrated MEMS tactile sensor comprising: a substrate, the substrate being a silicon wafer; a temperature sensor on the substrate, the temperature sensor comprising, from bottom to top, an electrically insulating layer and a thermistor, the electrically insulating layer being in direct contact with the thermistor; a pressure sensor on the substrate, the pressure sensor comprising, from bottom to top, an electrically insulating layer, a pressure chamber, and a piezoresistor, the electrically insulating layer being in direct contact with the pressure chamber and extending to the pressure chamber upper surface, the piezoresistor being on the pressure chamber upper surface and in direct contact with the extending electrically insulating layer; a pyroelectric infrared detector on the substrate, the pyroelectric infrared detector comprising, from bottom to top, an electrically insulating layer, a cavity, a central boss, a silicon nitride absorbing layer, and a thermocouple, the cavity being on the substrate, the central boss being in the center of the cavity, the silicon nitride absorbing layer being on the substrate and horizontally extending to the central boss upper surface, the silicon nitride absorbing layer being suspended directly above the cavity, the thermocouple being on the silicon nitride absorbing layer upper surface, the electrically insulating layer being in direct contact with the silicon nitride absorbing layer; a thermal conductive sensor on the substrate, the thermal conductive sensor comprising, from bottom to top, a lower silicon substrate, an upper silicon substrate, an electrically insulating layer, and a concentric chromium / platinum thin film layer, the lower silicon substrate being on the substrate, the upper silicon substrate comprising, from bottom to top, a bottom silicon layer, a porous material layer, a PDMS layer, and a top silicon layer, the bottom silicon layer being on the substrate, the porous material layer being on the bottom silicon layer, the PDMS layer being on the porous material layer, the top silicon layer being on the PDMS layer, the concentric chromium / platinum thin film layer being on the bottom silicon layer and the top silicon layer, respectively, the electrically insulating layer being on the lower silicon substrate and horizontally extending to the upper silicon substrate, the electrically insulating layer being suspended directly above the substrate, the electrically insulating layer being in direct contact with the concentric chromium / platinum thin film layer; the method comprising the following steps: manufacturing a 4-inch silicon wafer, doping the substrate by boron iron injection; then annealing the substrate in oxygen, maintaining at 1100°C for 65 minutes to activate the impurity doping and simultaneously obtain a 0.5 μm thick thermal oxide layer; next, depositing a 0.5 μm thick low-stress silicon nitride film by low-pressure chemical vapor deposition; the manufactured silicon dioxide / silicon nitride film acts as an electrically insulating layer for the pressure sensor and the temperature sensor; in the pyroelectric infrared detector part, removing the silicon dioxide / silicon nitride film by reactive ion etching to reduce the thickness of the final absorbing film. A 2 μm thick low temperature oxide and a 0.25 μm thick phosphosilicate glass are sequentially deposited and patterned by low pressure chemical vapor deposition; the phosphosilicate glass / low temperature oxide layer is used as a sacrificial structure for the pressure sensor; the low temperature oxide defines the gap between the functional layer and the substrate; the phosphosilicate glass layer covering the low temperature oxide accelerates the lateral etching rate, wherein the phosphorus content determines the etching rate; the lateral release holes are composed of phosphosilicate glass, facilitating the later sealing; A 1.2 μm thick LS-silicon nitride is deposited at 875 °C by low pressure chemical vapor deposition; the LS-silicon nitride multifunctional layer is used as a pressure chamber in the pressure sensor and an absorption film in the pyroelectric infrared detector; by adjusting the flow rate of the gas, the silicon-rich silicon nitride is adjusted to achieve a low residual tensile stress of about 100 MPa, measured by a laser scanning profilometer; then a 0.8 μm thick fine-grained polysilicon is deposited at 620 °C by low pressure chemical vapor deposition, followed by B+ implantation, and the polysilicon layer is patterned to form the piezoresistor, thermocouple and thermistor; next, the 1.2 μm thick LS-silicon nitride film is patterned by reactive ion etching to open the release holes for sacrificial layer etching; The sacrificial low temperature oxide layer is removed with 40% hydrofluoric acid for 8-10 minutes, and the etching process is checked under a microscope through a transparent silicon nitride membrane; a 1.4 μm thick tetraethyl orthosilicate is deposited by low pressure chemical vapor deposition and patterned by buffer oxide etching to seal the release holes; In an oxygen environment, annealing at 1100 °C for 1 hour obtains a uniform ion distribution in the polysilicon resistor with a sheet resistance of 100 Ω / sq; at the same time, a 0.4 μm thick thermal oxide is obtained outside the polysilicon, followed by deposition of a 0.2 μm thick LS-silicon nitride by low pressure chemical vapor deposition; next, the contact hole is opened by reactive ion etching, and a 0.6 μm thick aluminum layer is sputtered and patterned, which is used for interconnecting the thermocouple part of the pyroelectric infrared detector; at this point, the processing of the pressure sensor and temperature sensor is completed; The release groove of the pyroelectric infrared detector is opened, and the silicon substrate under the pyroelectric infrared detector absorption film and thermocouple is removed to a certain depth by bulk micromachining to achieve thermal insulation, and then the silicon is etched by a xenon difluoride isotropic dry etching process, wherein the xenon difluoride is 2 torr, the nitrogen is 60 torr, each cycle is set to 20 s, a total of 800 cycles are performed, and the etching depth is about 50 μm; at this point, the pyroelectric infrared detector is completed; Finally, a cover wafer with a reactive ion etching processing chamber is manufactured, coated with a 2 μm thick benzocyclobutene, and bonded to the cover wafer, which can protect the pyroelectric infrared detector during the subsequent cutting process; the piezoresistor and thermistor are placed outside the cover wafer; The concentric chromium / platinum thin film layer of the heat-conducting sensor is prepared by spin-coating 30 μm photoresist on a silicon plate, obtaining a pattern by photoetching and developing, sputtering 30 nm thick chromium as an adhesion layer, and then sputtering 150 nm thick platinum as a thermosensitive layer; the patterned substrate is immersed in acetone for 2 hours to dissolve the photoresist, then washed with anhydrous ethanol and deionized water, and finally a 4 μm thick parylene film is deposited on the patterned substrate as a protective layer; The porous material of the heat-conducting sensor is made of PDMS, citric acid monohydrate particles and silver nanoparticles; in the material preparation, the volume ratio of PDMS to citric acid monohydrate is 1:3, the volume ratio of PDMS to crosslinking agent is 10:1, and the volume ratio of silver nanoparticles is 2%; after the mixture is fully stirred for 10 minutes, it is poured into a PMMA mold and cured at 75°C for 2 hours; after demolding, the material is immersed in ethanol for 24 hours to dissolve citric acid monohydrate and form pores, then washed with deionized water, and finally dried at 70°C for 1 hour; finally, the sensing layer is adhered to the upper surface of the prepared PDMS layer and the lower surface of the porous material, and the heat-conducting sensor is completed.

2. The method of claim 1, wherein: The number of electrically insulating layers in the temperature sensor is 2, which are located below and in direct contact with the thermistor, and the electrically insulating layers and the thermistor are located on the substrate.

3. The method of claim 1, wherein: The pressure chamber in the pressure sensor is a cuboid structure, the inside of the pressure chamber is vacuum, the number of piezoresistors is 4, which are located on the upper surface of the pressure chamber and spaced apart by a certain distance, and the number of electrically insulating layers is also 4 and does not contact each other, which are located on the substrate and extend to the upper surface of the pressure chamber, and the electrically insulating layers are in direct contact with the pressure chamber and the piezoresistors.

4. The method of claim 1, wherein: The recessed cavity in the pyroelectric infrared detector is located on the substrate and is etched, the center boss is located at the center of the recessed cavity, the height of the center boss is equal to the depth of the recessed cavity, there are 15 silicon nitride absorption layers, which are distributed as follows: 4 on the upper left, 4 on the upper right, 4 on the lower left, and 3 on the lower right, the silicon nitride absorption layers are located on the substrate and horizontally extend to the upper surface of the center boss, the silicon nitride absorption layers are suspended above the recessed cavity, the number of thermocouples is also 15, which are distributed on the upper surfaces of the 15 silicon nitride absorption layers, the number of electrically insulating layers is 2, which are located on the lower right of the substrate, parallel to the remaining 3 silicon nitride absorption layers in the same direction, and horizontally extend to the upper surface of the center boss, and the electrically insulating layers are suspended above the recessed cavity.

5. The method of claim 1, wherein: The upper silicon substrate and the lower silicon substrate in the heat-conducting sensor have equal height and width, the lower silicon substrate is made of silicon only, the upper silicon substrate is composed of a bottom silicon layer, a porous material layer, a PDMS layer and a top silicon layer from bottom to top, the concentric chromium / platinum film layers are located on the bottom silicon layer and the top silicon layer respectively, the concentric chromium / platinum film layers are square, the number of the electrically insulating layers is 4, the electrically insulating layers are located on the lower silicon substrate and horizontally extend to the upper surface of the upper silicon substrate, and the electrically insulating layers are in direct contact with the four ends of the concentric chromium / platinum film layers respectively.

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