Foreword At the beginning of the new century, due to Firestone quality problems, a large number of punctures and overturn accidents caused more than 100 deaths and 400 injuries, which attracted the attention of the automotive industry and the U.S. government. The company had to recall 6.5 million tires in August of the following year. According to statistics, 260,000 traffic accidents in the United States each year are caused by low tire pressure or leakage, accounting for 75% of traffic accidents. And 70% of traffic accidents on China's highways are caused by punctures.
Tire quality experts believe that “maintaining a standard tire pressure and timely detection of tire leakage is the key to preventing tire puncture.†The current low-cost, hand-held digital tire pressure gauge cannot guarantee the timely detection of tire leaks. More than 2 million indirect measurement technologies on General Motors and Ford Motor Company's in-vehicle measurement technology—comparing the speed of each tire with a dead-end brake tire speed sensor—and deducing whether the tire pressure is insufficient or not is both cumbersome and inaccurate.
The smart tires with tire pressure monitoring sensors and radio frequency transmitters installed in each tire are attracting great attention. The smart tires are matched with a receiver and display on the dashboard of the car to form a tire pressure measuring system, namely TPMS. (TirePressureMonitoringSystem), it can also be called tire pressure monitoring sensor (TirePressureMonitoringSensor).
The US Federal Highway Administration’s mandatory federal decree in the mid-seventies of the last century contributed to the popularity of fuel injection systems and the culmination of the first automotive sensor applications. Another NHTSA Federal Act of 2002 stipulates that U.S. automobiles will assemble TPMS systems at a rate of 15%, 35%, 65%, and 100% each year from 2003 to 2006, which will set off a new wave of automotive pressure sensor applications. .
The unique working environment conditions of the tire pressure sensor tyres determine the high requirements of the pressure sensors for real-time monitoring of the tire pressure, require a high practical total accuracy within a wide temperature range, wide supply voltage range, low power consumption requirements, and wireless signal transmission requirements. , Resist harsh environment requirements and low cost requirements.
Motorola is an active developer of the TPMS system. It uses the MEMS-based silicon integrated capacitive pressure sensor MPXY8020A as a tire pressure detection unit, featuring low power consumption and full integration. The MC68HC908RF2 in a 32-pin package is used as a signal control processing and transmission unit. It is an 8-bit microcontroller and UHF transmitter integrated device, using MC33594 as a receiving unit.
GENovaSensor, a well-known sensor manufacturer acquired by General Electric in recent years, is another active developer. It employs a MEMS-based silicon piezoresistive pressure sensor as a tire pressure monitoring unit, and is equipped with a single control system. Measurement, signal compensation and adjustment and transmission of dedicated CMOS large-scale integrated circuits. Packaged in a standard 14-pin SOIC package, the two chips form a TPMS, model number NPXC01746. Due to the wake-up transient mode, the power consumption is only 9.7 microamps second, which can meet a ten-year working life of the battery. Due to the digital compensation function, the accuracy of the voltage measurement is better than 1.5% FS in the range of battery voltages from -40°C to +125°C from 2.1V to 3.0V. The greater significance of the Nova mode is that it can use existing ASICs. Integrate with any kind of integrated Whiston full bridge piezoresistive pressure sensor to produce more models of TPMS products.
SensoNor of Norway specializes in the manufacture of piezoresistive pressure-based integrated sensors manufactured by tire pressure monitoring system suppliers such as TRW Automotive, SmarTire, TPMS, SensoNor's piezoresistive tire sensors and SmarTire's RF generators. Successful TPMS It has been adopted by Siemens VDO Auto Parts and Goodyear.
Design and development of force sensor chip for tire pressure sensor To develop a tire pressure sensor, we designed and developed a suitable absolute pressure sensor, which is a miniature piezoresistive absolute pressure sensor based on MEMS silicon body micromachining technology. Sensitive components are integrated Whiston full bridge. The force-sensitive resistors are conventionally distributed on the center points of the four edges of the square silicon film and are arranged in the <110> crystal direction. One pair is in a longitudinal layout and the pair is in a tangential layout, thereby forming a Wheatstone strain full bridge. The width of the resistor strip is 8um and the total length is 60um. The average effective stress can guarantee the output sensitivity of 20mV/V. The resistor is formed by ion implantation doping and has excellent uniformity and doping accuracy to ensure the stability of zero and sensitivity. The impedance of the resistor design is 5KΩ. The silicon-silicon bonding technology is used to form the vacuum reference cavity of the absolute pressure sensor. Compared with the use of silicon-pyrex glass anode bonding to form an absolute pressure reference cavity, it has better thermal expansion system matching, and thus is more conducive to the thermal stability and time stability of the product. Another major advantage of using this design process technology is that the unit chip size can be greatly reduced. The unit chip size of this design is 1mm×1mm, and more than 7,000 force-sensing element units can be fabricated on a four-silicon wafer. The unit size of the silicon-glass bonded design is generally 1.5×1.5mm to 2.2×2.2mm, so the number of pressure-sensitive components that can be fabricated on a four-inch silicon wafer is 3400 and 1600 respectively. Obviously, Our design helps to reduce unit production costs. Of course, the precondition for adopting this design is to master silicon-silicon bonding technology and thin silicon film fabrication technology. In view of the large range of tire pressure sensors and thick silicon diaphragms, precision mechanical thinning or isotropic corrosion technology is not difficult to meet the design requirements, even if this design's range is extended to automotive MAP and AAP absolute pressure The range of the sensor, using SmartCut technology or epitaxial wafer electrochemical selective etching technology is not difficult to obtain 15 ~ 20um thick silicon film.
Nonlinearity: 0.05~0.1%FS; Hysteresis and repeatability: 0.03%FS; Output sensitivity: 10~20mV/V; Range: 700Kpa; Overload capability: 300%; Zero and sensitivity temperature coefficient: 1~3×10-4 /°C·FS.
The chip can also be used for tire pressure sensors and hand-held digital tire pressure and supporting use.
Conclusion The use of MEMS silicon micro-machining technology to produce tire pressure sensor chip for tire pressure monitoring system successfully, using silicon-silicon bonding design and related process technology to reduce chip size, reduce unit cost, and take the first step for TPMS product development .
Tire quality experts believe that “maintaining a standard tire pressure and timely detection of tire leakage is the key to preventing tire puncture.†The current low-cost, hand-held digital tire pressure gauge cannot guarantee the timely detection of tire leaks. More than 2 million indirect measurement technologies on General Motors and Ford Motor Company's in-vehicle measurement technology—comparing the speed of each tire with a dead-end brake tire speed sensor—and deducing whether the tire pressure is insufficient or not is both cumbersome and inaccurate.
The smart tires with tire pressure monitoring sensors and radio frequency transmitters installed in each tire are attracting great attention. The smart tires are matched with a receiver and display on the dashboard of the car to form a tire pressure measuring system, namely TPMS. (TirePressureMonitoringSystem), it can also be called tire pressure monitoring sensor (TirePressureMonitoringSensor).
The US Federal Highway Administration’s mandatory federal decree in the mid-seventies of the last century contributed to the popularity of fuel injection systems and the culmination of the first automotive sensor applications. Another NHTSA Federal Act of 2002 stipulates that U.S. automobiles will assemble TPMS systems at a rate of 15%, 35%, 65%, and 100% each year from 2003 to 2006, which will set off a new wave of automotive pressure sensor applications. .
The unique working environment conditions of the tire pressure sensor tyres determine the high requirements of the pressure sensors for real-time monitoring of the tire pressure, require a high practical total accuracy within a wide temperature range, wide supply voltage range, low power consumption requirements, and wireless signal transmission requirements. , Resist harsh environment requirements and low cost requirements.
Motorola is an active developer of the TPMS system. It uses the MEMS-based silicon integrated capacitive pressure sensor MPXY8020A as a tire pressure detection unit, featuring low power consumption and full integration. The MC68HC908RF2 in a 32-pin package is used as a signal control processing and transmission unit. It is an 8-bit microcontroller and UHF transmitter integrated device, using MC33594 as a receiving unit.
GENovaSensor, a well-known sensor manufacturer acquired by General Electric in recent years, is another active developer. It employs a MEMS-based silicon piezoresistive pressure sensor as a tire pressure monitoring unit, and is equipped with a single control system. Measurement, signal compensation and adjustment and transmission of dedicated CMOS large-scale integrated circuits. Packaged in a standard 14-pin SOIC package, the two chips form a TPMS, model number NPXC01746. Due to the wake-up transient mode, the power consumption is only 9.7 microamps second, which can meet a ten-year working life of the battery. Due to the digital compensation function, the accuracy of the voltage measurement is better than 1.5% FS in the range of battery voltages from -40°C to +125°C from 2.1V to 3.0V. The greater significance of the Nova mode is that it can use existing ASICs. Integrate with any kind of integrated Whiston full bridge piezoresistive pressure sensor to produce more models of TPMS products.
SensoNor of Norway specializes in the manufacture of piezoresistive pressure-based integrated sensors manufactured by tire pressure monitoring system suppliers such as TRW Automotive, SmarTire, TPMS, SensoNor's piezoresistive tire sensors and SmarTire's RF generators. Successful TPMS It has been adopted by Siemens VDO Auto Parts and Goodyear.
Design and development of force sensor chip for tire pressure sensor To develop a tire pressure sensor, we designed and developed a suitable absolute pressure sensor, which is a miniature piezoresistive absolute pressure sensor based on MEMS silicon body micromachining technology. Sensitive components are integrated Whiston full bridge. The force-sensitive resistors are conventionally distributed on the center points of the four edges of the square silicon film and are arranged in the <110> crystal direction. One pair is in a longitudinal layout and the pair is in a tangential layout, thereby forming a Wheatstone strain full bridge. The width of the resistor strip is 8um and the total length is 60um. The average effective stress can guarantee the output sensitivity of 20mV/V. The resistor is formed by ion implantation doping and has excellent uniformity and doping accuracy to ensure the stability of zero and sensitivity. The impedance of the resistor design is 5KΩ. The silicon-silicon bonding technology is used to form the vacuum reference cavity of the absolute pressure sensor. Compared with the use of silicon-pyrex glass anode bonding to form an absolute pressure reference cavity, it has better thermal expansion system matching, and thus is more conducive to the thermal stability and time stability of the product. Another major advantage of using this design process technology is that the unit chip size can be greatly reduced. The unit chip size of this design is 1mm×1mm, and more than 7,000 force-sensing element units can be fabricated on a four-silicon wafer. The unit size of the silicon-glass bonded design is generally 1.5×1.5mm to 2.2×2.2mm, so the number of pressure-sensitive components that can be fabricated on a four-inch silicon wafer is 3400 and 1600 respectively. Obviously, Our design helps to reduce unit production costs. Of course, the precondition for adopting this design is to master silicon-silicon bonding technology and thin silicon film fabrication technology. In view of the large range of tire pressure sensors and thick silicon diaphragms, precision mechanical thinning or isotropic corrosion technology is not difficult to meet the design requirements, even if this design's range is extended to automotive MAP and AAP absolute pressure The range of the sensor, using SmartCut technology or epitaxial wafer electrochemical selective etching technology is not difficult to obtain 15 ~ 20um thick silicon film.
Nonlinearity: 0.05~0.1%FS; Hysteresis and repeatability: 0.03%FS; Output sensitivity: 10~20mV/V; Range: 700Kpa; Overload capability: 300%; Zero and sensitivity temperature coefficient: 1~3×10-4 /°C·FS.
The chip can also be used for tire pressure sensors and hand-held digital tire pressure and supporting use.
Conclusion The use of MEMS silicon micro-machining technology to produce tire pressure sensor chip for tire pressure monitoring system successfully, using silicon-silicon bonding design and related process technology to reduce chip size, reduce unit cost, and take the first step for TPMS product development .
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