Papers by Keyword: Circular Diaphragm

Abstract: A new idea is presented which develops a general model predicting the deflection profile of clamped circular diaphragm of Capacitive Micromachined Ultrasonic Transducers (CMUTs) in order to calculate its capacitance. The CMUTs we consider is made of silicon nitride material which is widely used because of its low intrinsic stress. And the general model proposed in this paper is highly accurate in predicting the deformed membranes and exhibits excellent agreement with 3D-FEA results in capacitance deviation less than 1%. These new established deflection functions can be used to implement a much higher accurate design methodology for CMUTs and other MEMS-based capacitive type sensors built with circular diaphragm.

Abstract: This paper presents a MEMS Piezoresistive pressure sensor which utilizes a circular shaped polysilicon diaphragm with a nanowire to enhance the sensitivity of the pressure sensor. The polysilicon nanowire is fabricated in such a way that it forms a bridge between the circular polysilicon diaphragm and the substrate. The high Piezoresistive effect of Silicon nanowires is used to enhance the sensitivity. A circular polysilicon nanowire piezoresistor was fabricated by means of reactive ion etching. This paper describes the performance analysis, structural design and fabrication of piezoresistive pressure sensor using simulation technique. The polysilicon nanowire pressure sensor has a circular diaphragm of 500nm radius and has a thickness about 10nm. Finite element method (FEM) is adopted to optimize the sensor output and to improve the sensitivity of the circular shaped diaphragm of a polysilicon nanowire Piezoresistive pressure sensor. The best position to place the Polysilicon nanowires to receive maximum stress was also considered during the design process..The fabricated polysilicon nanowire has high sensitivity of about 133 mV/VKPa.

Abstract: A pressure sensor in the range of 25 MPa with circular diaphragm is designed and fabricated, and the calibration experiments prove its excellent performance, which also reflects the correct choice of design after analyzing the effect of diaphragm dimension, location and shapes of piezoresistors. Circular diaphragms of different thickness and diameters are simulated to meet the pressure requirement of 25 MPa. It also displays the advantage of piezoresistive sensors over others and the difference characteristics between different types of piezoresistive sensors. And then the effect of piezoresistor location is analyzed and simulated to attain high accuracy and sensitivity after the circular diaphragm chip is packaged with borosilicate glass ring. The whole fabrication process of the chip is inexpensive and compatible with standard MEMS process. The experimental results show the developed high pressure sensor with the sensitivity of 2.533 mV/MPa has excellent performance, such as linearity of 0.08%FS, hysteresis of 0.03%FS, accuracy of 0.11%FS and repeatability of 0.03%FS under high temperature of 200 °C.

Abstract: Single crystal silicon diaphragms are widely used as pressure sensitive elements in micromachined pressure sensors. When designing such a sensor it is usual to assume that the silicon is an isotropic material and the average elastic constants are used. However, the mechanical properties of single crystal silicon are orthotropic, and this has an important effect on the mechanical behaviour of silicon diaphragms under pressure. In this work, the deflections of orthotropic silicon circular diaphragms which are orientated against the (100) and the (110) planes are presented. It is found that by assuming silicon is isotropic material, the maximum stress is underestimated by 9.4% for (110) orientated silicon diaphragms, while the maximum stress is underestimated by 8% for (100) orientated silicon diaphragms. Therefore, when a silicon diaphragm is used in a MEMS sensor, the orthotropic properties should be taken into account for accuracy. Finally, the performance of a capacitive sensor is predicted by using finite element method.