Huiwang Lin

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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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.

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

In this study, 50 nm-thick ZrO2 thin films have been prepared on Si substrate by liquid delivery metal-organic chemical vapor deposition(LD-MOCVD) at 650°C. The structural characteristics of the samples were investigated by X-ray diffraction analysis and SEM respectively, showed a tetragonal phase and a high uniformity of ZrO2 films. The electrical properties were studied by C-V and I-V measurements on Au/ZrO2/Si Metal-Insulator-Semiconductor (MIS) structure. The dielectric constant of ZrO2 films was 15. The leakage current-voltage dependence showed 3 different conduction mechanisms, which were Poole-Frenkel conduction mechanism, Schottky emission mechanism or ohmic emission.

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

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

The Structure and Characterization of ZrO2 Thin Films Prepared by Liquid Delivery-MOCVD

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.

A novel MOSFET pressure microsensor

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

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

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.

A Novel Combined Pressure/Temperature Microsensor

Much has been done in improving the performance of piezoresistive pressure sensors in various aspects. It is also important to realize good consistency among different device units on a big wafer under the circumstance that the manufacture of piezoresistive pressure sensors is highly industrialized. Bad product consistency results from processing deviation which is hard to control and can never be reduced to zero. An effective approach to reduce the influence of processing deviation on sensitivity of pressure sensors is provided in this paper: properly enlarging the size of the square silicon diaphragm. Finite element analysis (FEA) is basically used in the work. Test results show that relative errors for sensitivity of pressure sensors with diaphragm of larger size(length of 300um) are limited within 2.2% while pressure sensors with diaphragm of smaller size(length of 200um) from the same wafer have relative errors for sensitivity varying a lot, from 0.1% to 32.2%.

A Low Power Consumption Tire Pressure Monitoring System

in Silicon Bonding Gu-Jin Miao, Zhao-Hua Zhang, Tian-Ling Ren, Hui-Wang Lin, Li-Tian Liu Institute of Microelectronics, Tsinghua University Tsinghua National Laboratory for Information Science and Technology, Beijing China Introduction: Traditionally, the energy of the bonding interface was measured at various levels, such as crackopening and IR camera detection. But crackopening is a destructive way to measure the bonding energy, even sometimes the value is not the adhesive energy of the bonding interface, but the bulk of the silicon. Although IR camera detection is a nondestructive way to research the bonding interface, it is also confined by its limited resolution. Actually, IR image only tells whether two surfaces are optical contacted in the micro-regional at micron level, without reflecting the exact bonding ability. Recently, HF etching has been proposed. But we think etching result is highly correlated with the distribution of the oxygen in the interface. However, no matter for electrical device or other applications, bonding technology does not only need optical contact, but also bonds with enough energy between the optical contacting surfaces. Electrical properties measurement, including I-V and C-V characteristics give a promising way to detect the voids and measure the energy of the interface. We want to corroborate the relationship between the bondability and the electrical characteristics of the interface (SiO2/Si).