Zhaohua Zhang

A Novel Pressure Microsensor With 30-

A novel pressure microsensor is designed, fabricated and tested. Novel piezoresistive sensing structures using 30- mum thick silicon diaphragms (from 370 mum times 370 mum to 970 mum times 970 mum ) and meander-shaped piezoresistors are devised. The diaphragms in this work thicker than that of the conventional piezoresistive pressure sensors extend the high-stress distribution into the bulk silicon and improve the device reliability. Piezoresistors are partially fabricated on the high-stress bulk silicon to obtain high sensitivity and linearity. Effects of different diaphragm areas, piezoresistor shapes, and placing methods on the sensing performances are simulated, measured, and analyzed. The whole fabrication is low-cost and compatible with standard IC process. Measurement shows promising results, i.e., large test region (0-1 MPa), high sensitivity (70.4 mV/VldrFS ), small linearity error (0.012%/FS) and good precision (0.16%/FS). The work indicates a novel solution of small size, high-performance, high-reliability, and low-cost pressure microsensor for tire pressure monitoring system and many other applications.

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A novel MOSFET pressure sensor was proposed based on the MOSFET stress sensitive phenomenon, in which the source-drain current changes with the stress in channel region. Two MOSFETpsilas and two piezoresistors were employed to form a Wheatstone bridge served as sensitive unit in the novel sensor. Compared with the traditional piezoresistive pressure sensor, this MOSFET sensorpsilas sensitivity is improved significantly, meanwhile the power consumption can be decreased. The fabrication of the novel pressure sensor is low-cost and compatible with standard IC process. It shows the great promising application of MOSFET-bridge-circuit structure for the high performance pressure sensor. This kind of MEMS pressure sensor with signal process circuit on the same chip can be used in positive or negative tire pressure monitoring system (TPMS) which is very hot in automotive electron research field.

-Thick Diaphragm and Meander-Shaped Piezoresistors Partially Distributed on High-Stress Bulk Silicon Region

Novel piezoresistive microsensors for automotive tire pressure monitoring system (TPMS) are designed, fabricated and tested. 30 mum thick silicon diaphragms (from 370 mum times 370 mum to 970 mum times 970 mum) are adopted, thicker than that of the conventional piezoresistive pressure sensor, which extends the high stress distribution in the bulk silicon. Novel meander shape piezoresistors are designed, parts of which are fabricated on the high stress bulk silicon to obtain high linearity and sensitivity. Different diaphragm areas, piezoresistive shapes and placing methods on the microsensor performances are simulated, measured and analyzed. The whole fabrication is low-cost and compatible with standard IC process, which tolerates large process variations. Good microsensor precision (0.23%/FS) is obtained. The whole work indicates a novel solution of small size, high performance and low cost piezoresistive microsensor for TPMS and many other applications.

A novel MEMS pressure sensor with MOSFET on chip

A novel MOSFET pressure sensor is firstly proposed based on the MOSFET stress sensitive phenomenon, in which the source-drain current changes with the stress in channel region. It uses two MOSFETs and two piezoresistors to form a Wheatstone bridge. Compared with the traditional piezoresistive pressure sensor, this MOSFET sensors sensitivity is improved significantly, meanwhile the power can be decreased. The fabrication is low-cost and compatible with standard IC process. It shows the great promising application of MOSFET-bridge-circuit structure for the high performance pressure microsensors

Design, Fabrication and Characterization of Novel Piezoresistive Pressure Microsensor for TPMS

A digital pressure sensor using a double-gate MOSFET mixer is presented. The sensitive unit of this pressure sensor is comprised of MOS ring oscillators. The syntonic frequency of the ring oscillators will change according to the stress caused by pressure due to the MOSFET piezoresistive effect. The double-gate MOSFET mixer is used as an internal signal processor in order to improve the characteristics of the output signal. The pressure sensor has many good characteristics such as high sensitivity, low temperature coefficient and simple fabrication process. The device was fabricated by a standard IC process mixed with a MEMS process. The sensitivity of fabricated devices is 1.52 kHz/kPa. The temperature shift of zero output is -0.5% FS.

A novel MOSFET pressure microsensor

Sensitivity is one of the most important parameters for piezoresistive pressure sensors. It is usually through superior design of the full scale output of pressure sensors to achieve high sensitivity of the devices and meet the requirement for certain application. Two kinds of methods of evaluating the full scale output of pressure sensors are discussed .Both of them are based on finite element analysis (FEA) and integration of stress difference with respect to certain path, which are realized by ANSYS. In addition, results of these two methods are coincident with each other. The full scale output of the pressure sensor by simulation is 42.996mv while the best result from experiment is 43.112mv. For all the experiment results, relative errors are limited to 2.5%. Therefore the experiment results show good agreement with the simulation results.

The application of double-gate MOSFET mixer in digital pressure sensor

A novel structure based on cancellation was presented for linearizing amplifiers. This robust circuit compensates high order nonlinearity by 4-phase offset signals. A third order specified example was illustrated. Theoretically, the third order nonlinearity would be totally eliminated when using the proposed arrangement. It is especially designed for large swing signals and low power application. An on chip filter for MEMS sensor interface verified the principle. In practice, it was observed that the total harmonic distortion level was reduced up to 13.5db.

Methods of Superior Design for the Full Scale Output of Piezoresistive Pressure Sensors

A multi-frequency wireless passive pressure sensor was developed for tire pressure monitoring system. The applied sensor was fabricated with SAW delay lines on a membrane, which produced enhanced sensitivity and accuracy by means of multiple frequency Continues Wave. The SAW elements operate at two frequencies in 434 MHz band. The pressure is determined by calculating the reflective phase difference between the two frequencies. This new method avoids phase ambiguity and temperature dependence due to large membrane bending and temperature variation, and therefore enhances the sensor sensitivity and accuracy. In this paper, the implementation of the Tire Pressure Monitoring System (TPMS) comprising remote sensor fabrication, interrogator structure and signal processing algorithm were described. Issues about sensor calibration were also discussed. This sensor attained superior high pressure sensitivity and lower system complexity compared to conventional SAW sensors, and is very suitable for TPMS.

Amplifier high linearization method based on offset cancellation technique

A novel microsensor combining piezoresistive and thermal resistive components is designed and fabricated. A 50mum thick silicon diaphragm (500mumtimes500mum) is used, thicker than that of the conventional piezoresistive pressure sensor, which extends the high stress distribution in the bulk silicon, and increases the operating range as well as the burst pressure. Novel meander shape piezoresistors are designed with optimized structure parameters, parts of which are fabricated on the high stress bulk silicon to obtain high sensitivity. Effects of different fabrication parameters on bulk silicon thermistor performances are compared, and the same implantation process with piezoresistors is chosen. Good temperature linearity and sensitivity are obtained, and the fabrication is simplified. The whole fabrication is low-cost and compatible with standard IC process, which tolerates large process variations. Primary measured results are presented

A multi-frequency wireless passive pressure sensor for TPMS applications

TPMS (Tire Pressure Monitoring System) is a typical automobile-electronic system used to prevent traffic accident. In this paper, a TPMS with low-power consumption is designed and realized. It is a direct TPMS. This system is made up of Tire Transmitting Module and Central Receiving Module. Tire Transmitting Module can monitor the pressure and temperature of each tire when the car is running. In order to achieve low power consumption, a vibration switch and a Power Management Module is applied in Tire Transmitting Module. An intermittent work process is designed to reduce the power consumption. The system can give warnings of different abnormal situations (low pressure, high pressure and leakage of pressure) until the pressure returns to normal. In theory, the life of the system is more than 3 years.