Kyoichi Ikeda

Silicon pressure sensor integrates resonant strain gauge on diaphragm

Abstract A novel silicon pressure sensor has been developed which will enable high-precision pressure measurement. The sensor, which is based on a new concept, is fabricated from a single silicon crystal and has two resonant strain gauges which are held in vacuum cavities on the surface of the diaphragm to isolate them from the surrounding fluid. The two oscillating frequencies of the resonant strain gauges are differentially modulated by pressure. The sensors measuring principle, features, its amplitude-controlled self-oscillation circuit, and the results of experiments are given.

Vacuum-sealed silicon micromachined pressure sensors

Considerable progress in silicon pressure sensors has been made in recent years. This paper discusses three types of vacuum-sealed silicon micromachined pressure sensors that represent the present state of the art in this important area. The devices are a capacitive vacuum sensor, a surface-micromachined microdiaphragm pressure sensor, and a resonant pressure sensor. Vacuum sealing for these devices is accomplished using anodic bonding, films deposited using low-pressure chemical vapor deposition, and thermal out-diffusion of hydrogen, respectively. These sensors emphasize high sensitivity, small size, and excellent stability, respectively. The silicon-diaphragm vacuum sensor uses electrostatic force balancing to achieve a wide pressure measurement range.

Three-dimensional micromachining of silicon pressure sensor integrating resonant strain gauge on diaphragm

Abstract A method of fabricating a novel pressure sensor is presented. The sensor has resonant strain gauges built into micro vacuum cavities on the surface of the diaphragm. The resonant strain gauge has a resonator the natural frequency of which is modulated by the strain in the diaphragm surface. The resonator and the vacuum cavity of the strain gauge are fabricated by a self-aligning selective epitaxial method and a hybrid selective etching method; a unique vacuum-sealing technique is used to make the vacuum cavity.

Various applications of resonant pressure sensor chip based on 3-D micromachining

Abstract An accurate and stable resonant pressure sensor fabricated using 3-D micromachining process was developed. Two resonators are located on the surface of the diaphragm and applied pressure is measured from the difference of two resonant frequencies. The resonators are encapsulated into the micro-vacuum cavities in order to isolate them from surrounding fluid and to get stable resonance. Three components, namely, the diaphragm, the resonators, and the vacuum cavities, are all single crystalline and monolithically structured on the 6.8×6.8-mm wide, 0.5-mm thick silicon chip. The resonator, having a high Q -value of 50 000, was obtained owing to the vacuum isolation and resulted in superior characteristics such as resolution, repeatability and long-term stability. In the next place, the developed pressure sensor was successfully applied to the differential pressure transmitter for industrial process, and several further applications were accomplished successively.

Photo-induced preferential anodization for fabrication of monocrystalline micromechanical structures

Photo-induced preferential anodization (PIPA) for fabrication of monocrystalline micromechanical structures is presented. P-type silicon formed in an n-type substrate is preferentially anodized in an aqueous solution of hydrofluoric acid under illumination. This technology is based on anodization and the photovoltaic effect. In experiments, dependence on light intensity, HF concentration, and the ratio of the pn-junction area to the entrance area of the HF solution was investigated. It was found that porous silicon conditions depend on light intensity and HF concentration and that anodic current density provided by a pn-junction is the most important factor for controlling PIPA. A monocrystalline microbridge structure 1 mu m thick, 20 mu m wide, and 300 mu m long was formed using this technology.<<ETX>>

Strain sensitive resonant gate transistor

The strain sensitive resonant gate transistor working as a strain gauge has been developed. This device is fabricated by using surface micro-machining techniques and CMOS technology. Poly-Si bridge is fixed to the FET structures and the bridge is encapsulated by a Poly-Si cell in order to keep it inside the vacuum. When the strain is applied to the bridge, the resonant frequency is changed. The shift of resonant frequency is converted to the frequency of alternating drain current. Some basically technological problems are in order to realize high sensitivity and reliability in this sensor. As a result, the strain sensitive sensor with the characterizations of high gage factor, high Q factor, no-sticking and wide-working-range is developed. Characterizations of this sensor have been demonstrated.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.The strain sensitive resonant gate transistor working as a strain gauge has been developed. This device is fabricated by using surface micro-machining techniques and CMOS technology. Poly-Si bridge is fixed to the FET structures and the bridge is encapsulated by a Poly-Si cell in order to keep it inside the vacuum. When the strain is applied to the bridge, the resonant frequency is changed. The shift of resonant frequency is converted to the frequency of alternating drain current. Some basically technological problems are in order to realize high sensitivity and reliability in this sensor. As a result, the strain sensitive sensor with the characterizations of high gage factor, high Q factor, no-sticking and wide-working-range is developed. Characterizations of this sensor have been demonstrated.

Electromagnetically driven silicon microvalve for large-flow pneumatic controls

The authors report a large-flow microvalve which has an ability to replace conventional pneumatic control devices. The authors have analyzed the generating force for various driving methods and concluded a combination of silicon micromachined valve structure and electromagnetic driving is the best way for the large-flow control. The electro- magnetic actuator consists of an externally placed solenoid and a magnetic metal chip which is bonded to silicon valve chip. The actuator produces force larger than 0.1 N along 0.1 mm stroke. The valve structure is integrated on the silicon chip, which consists of an anisotropically etched orifice and a polysilicon valve sheet with springs. The polysilicon layer has a 30 micrometers thickness designed to obtain a strong structure enough to be operated with large force and large displacement. This microvalve can control large-flow gases with short response time and low power consumption, owing to electromagnetic driving. Moreover, the integration of the valve parts reduces its cost and assembly processes. The measured results show that 8.8 1/min air flow is controlled at 440 kPa by 210 mW electric power consumption and the response time is less than 3 ms, which are difficult to achieve by microvalves reported so far.

Differential Pressure Sensor With Micromachined Overrange Protectors

A differential pressure sensor which has protectors on both sides for overrange pressure is presented. There are two narrow gaps (-lpm) on both sides of a square diaphragm on the sensor. When the overrange pressure is applied, the diaphragm contacts the planes which face the narrow gaps and is protected from fracturing. The sensor also works as a high-pressure vessel and a hermetically sealed electrical feedthrough. An overhang structure was created to improve the strength of the bonded structure of a silicon chip and a pyrex glass base. These structures are integrated with a silicon sensor chip using micromachining technology. The measurement range of the sensor is f100kPa and the sensor withstands an overrange differential pressure and static pressure which are a few hundred times over the measurement range.