Zhang Zhaohua

Simulation and design of micro pressure sensors applied to measure the intracranial pressure

This paper reports a micrometer level pressure sensor to measure the intracranial pressure (ICP). The sensor is based on the piezoresistive effect. The piezoresistive pressure sensor is simulated and designed by using nonlinear programming Optimizing and Finite Element Analysis (FEA) tools. The sensor is fabricated by MEMS process. From tests, the sensor samples performances match up the design.

Low Power and High Sensitivity MOSFET-Based Pressure Sensor

Based on the metal-oxide-semiconductor field effect transistor (MOSFET) stress sensitive phenomenon, a low power MOSFET pressure sensor is proposed. Compared with the traditional piezoresistive pressure sensor, the present pressure sensor displays high performances on sensitivity and power consumption. The sensitivity of the MOSFET sensor is raised by 87%, meanwhile the power consumption is decreased by 20%.

A novel dual-functional MEMS sensor integrating both pressure and temperature units

This paper proposes a novel miniature dual-functional sensor integrating both pressure and temperature sensitive units on a single chip. The device wafer of SOI is used as a pizeoresistive diaphragm which features excellent consistency in thickness. The conventional anisotropic wet etching has been abandoned, while ICP etching has been employed to etch out the reference cave to minimize the area of individual device in the way that the 57.4° slope has been eliminated. As a result, the average cost of the single chip is reduced. Two PN junctions with constant ratio of the areas of depletion regions have also been integrated on the same chip to serve as a temperature sensor, and each PN junction shows high linearity over −40 to 100 °C and low power consumption. The iron implanting process for PN junction is exactly compatible with the piezoresistor, with no additional expenditure. The pressure sensitivity is 86 mV/MPa, while temperature sensitivity is 1.43 mV/°C, both complying with the design objective.

Accelerometer Design Using MOS Ring Oscillator

A digital accelerometer is developed by using a ring oscillator (RO) and a mixer. The sensitive unit of the accelerometer is the metal-oxide semiconductor (MOS) ROs located on silicon beams. Based on the piezoresistive effect of the MOS RO, the accelerometer transduces the acceleration into frequency output. The syntonic frequency of the MOS RO changes in relation to many environmental elements, such as temperature, source voltage, and so on. The mixer is an interior signal processor that improves the output signal characteristics, with the digital output signal representing the frequency change. As the accelerometer is based on the piezoresistive effect of the MOS RO, the frequency characteristics of the MOS RO and its relationship with the acceleration are described. The device has been fabricated using standard integrated circuits processing methods combined with the Micro-Electro-Mechanical Systems process. The characteristics of the sample chip are in agreement with the theoretical predictions. The accelerometer has a high sensitivity of 6.91 kHz/g, a low temperature coefficient, and a simple fabrication process.

A novel accelerometer using MOS ring oscillators

Piezoresistive silicon accelerometers have many excellent performance characteristics such as high sensitivity, high reliability and low cost. In this paper, a novel piezoresistive silicon accelerometer using MOS ring oscillators is described and analysed. This accelerometer consists of two MOS ring oscillators, a mixer and a filter. Using a ring oscillator, the input acceleration changed into digital frequency output signal, this makes it easy to be used in digital world. The mechanical structure of this accelerometer is made up of one mass and four beams. Such structure can not only decrease cross-axis sensitivity, but also utilize the strain caused by input acceleration. Using finite-element analysis (FEA) software, we did strain simulation in order to analyse the stress distribution. The result of finite-element method simulation accorded with theory analysis very much. The MOS ring oscillator consists of an odd number of inverting gates connected in a ring and can be realized by CMOS, NMOS or PMOS circuits. The different kinds of MOS ring oscillator have different performances. Since MOS FET can realize the function of mixing frequency, the mixer is made up of MOS FET.