Silicon Micromachined Vacuum Encapsulated Resonant Pressure Sensors

Abstract

Silicon micromachined vacuum encapsulated resonant pressure sensors have been realized and have given several significant solutions for the problems by which the conventional metallic bulk machined resonant sensors have been worried. The problems includes the interference from environmental fluids where resonators are exposed. The interference reduces the quality factor of the resonator and alters the resonant frequency of the resonator. In this paper encapsulated resonant sensors. describes the solutions for the problems by silicon micromachined vacuum Introduction: Accuracy of a resonant sensor is proportional to the quality factor of the resonator. A silicon micromachined vacuum encapsulated resonator has a structure consisted from a micro resonator with in a vacuum micro cavity which isolates the resonator from external fluid. The structure has been realized by using micromachine technology. The technology has made the resonators' application fields extremely spread and has drastically brought manufacturing cost reduction of resonant sensors. The followings give a short review of silicon micromachined vacuum encapsulated resonant pressure sensors. Principle of Resonant Pressure Sensor: A resonant frequency of a bridge of which both ends are f+ed to a surface of a diaphragm is where E; Young's modulus p ; the density I; the moment of inertia A the area of cross section 1; the length of the bridge h; the thickness of the bridge e; strain by applied pressure S; strain sensitivity expressed by Es.(2) n; resonant mode number 12n2 (3' S = n2 (n + 1 / 2)4 From Eq.(l) applied strain (pressure) is proportional to square of the resonant frequency. Generally resonant frequency is obtained by measuring of frequency of self-