Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
1999-05-05
2001-07-24
Chapman, John E. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C073S514320, C073S514330, C073S514340
Reexamination Certificate
active
06263735
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an acceleration sensor for use in the control of a vehicle body and the like application fields. The invention also includes the producing method. In accordance with the invention, a high precision acceleration sensor is presented at a low cost, without using high-level semiconductor technologies or micro-machining technologies.
BACKGROUND ART
When an external force is given to a mass substance, acceleration is caused with the mass substance, at the same time an inertial force is observed for trying to retain the mass substance in the same location. The force given to a mass substance and an acceleration can be measured through a physical strain created by the inertial force. There have been a number of teachings on the method of detecting the strain. For example, a publication (Acceleration Sensor by Semiconductor, by Toshitaka SHIBATA, “Technology for Sensor”, Vol. 11, No. 10, October, 1991) discloses a sensor formed on a silicon material, which sensor being manufactured using semiconductor technologies and micro-machining technologies. Means for detecting the strain includes the one which makes use of the change in the electrostatic capacitance, and the one which makes use of the piezoresistance effect, for example. Acceleration sensors using a single crystal silicon for the sensing portion have a stable performance and are capable of measuring the acceleration at high precision level. Therefore, the sensors of the above category form the mainstream in the recent field of acceleration sensors.
Processing a silicon substrate with a high precision level into a certain specific shape, however, needs the help of the high-level semiconductor technologies and the micro-machining technologies. Therefore, acceleration sensors are costly at present. Conventional sensors, as taught in a publication (Micromechanical Acceleromater Integrated with MOS Detection Circuitry, KURTE, PETERSEN etc. IEEE TRANSACTION ON ELECTRON DEVICES, VOL. ED-29, No 1, JANUARY 1982) and other publications, contain an etching-stop layer in the silicon substrate, and the monocrystalline silicon has to be epitaxially grown. These are the essential requirements to be fulfilled in order to form a hinge portion, or the portion strained by an acceleration, of a sensor. Expensive semiconductor manufacturing facilities are needed to carry out the above described process steps.
Japanese Laid-open Patent No.05-340957 discloses a method of joining an auxiliary glass substrate to a silicon substrate forming the hinge portion by anode bonding. However, the anode bonding method requires a facility for providing electric fields among the bonding substrates. Furthermore, the anode bonding is available only with a glass that contains sodium. The anode bonding method is not simple to practice, and restrictive in selecting the glass material.
Another type of acceleration sensor uses a piezoelectric element for the portion at which a strain is caused by acceleration. However, it is difficult for an acceleration sensor of the above type to measure a static acceleration; such as the measurement of an inclination relative to the gravity of the earth. In some cases, an acceleration sensor is required to have a self-diagnostic function. Most of such self-diagnostic functions require to have complicated peripheral circuits.
The present invention addresses the above described drawbacks, and aims to offer an inexpensive, yet highly accurate, acceleration sensor formed of silicon and other materials, without asking for the help of the high level semiconductor technologies or the micro-machining technologies. The acceleration sensor in accordance with the present invention covers a wide range of the frequency in acceleration measurement, and is capable of making a self-diagnosis about a disorder. The present invention also offers a method for manufacturing such acceleration sensors.
DISCLOSURE OF THE INVENTION
In an invented acceleration sensor, only the hinge portion of a sensor section, which portion is strained by an acceleration force, is formed of silicon; while the auxiliary portions, a cover and a mass substance for receiving the acceleration are structured of glass or other materials. Joining of the different materials is conducted by direct bonding. The direct bonding is a technology that joins different kinds of materials by simply making the bonding surfaces ultra-clean. The direct bonding technology assures a firm joining between the materials themselves, by making the bonding surfaces clean and heating the surfaces at a high temperature in the atmospheric environment or in the vacuum; without intervening any foreign material, such as an adhesive substance, or providing any electric fields which were essential in the anode bonding. Thus the direct bonding produces a rigid joining at an inexpensive cost. The direct bonding can join silicon, glass, non-alkaline glass, quartz glass and various monocrystalline substrates together.
The hinge portion of said silicon substrate has to be processed to as thin as 10-30 &mgr;m thick. Joining a glass substrate to one surface of the silicon substrate by direct bonding and then grinding only the surface of silicon substrate may provide such a thin silicon substrate. In accordance with a recent grinding technology, a substrate can be ground down to approximately 10 &mgr;m at an accuracy level within ±1 &mgr;m. The accuracy level is high enough for processing the acceleration sensor of the present invention.
After the process for thinning the silicon substrate is finished, another glass plate is joined onto the silicon surface by direct bonding as the auxiliary substrate of the opposite surface. And then, a portion of mass substance for receiving an acceleration and a portion of hinge for yielding a strain are formed through etching process. Finally, a case is bonded from the both sides by direct bonding. The portion of mass substance and the portion of hinge were provided conventionally in the form of a one-piece silicon member manufactured out of a silicon substrate using high level micro-machining technologies. Now in an acceleration sensor of the present invention, the corresponding member is formed of different kinds of materials; glass for the mass substance portion and silicon for the hinge portion. As a result, etching of the member becomes easier, and the whole manufacturing process is simplified. By further providing a piezoelectric element, or a piezoresistive element, formed on the hinge portion, and attaching a glass case having an electrode for electrostatic capacitance in the corresponding area together, an acceleration sensor will have both of the features of electrostatic capacitance type and piezoelectric element type, or piezoresistive element type. Thus, acceleration sensors that can measure the acceleration for a wide range of frequency, capable of making the self-diagnosis can be manufactured efficiently with a high production yield rate.
REFERENCES:
patent: 5006487 (1991-04-01), Stokes
patent: 5060504 (1991-10-01), White et al.
patent: 5313836 (1994-05-01), Fujii et al.
patent: 5623099 (1997-04-01), Schuster et al.
patent: 4-089577 (1992-03-01), None
patent: 4-094186 (1992-03-01), None
patent: 5-119060 (1993-05-01), None
patent: 5-340957 (1993-12-01), None
patent: 6-160420 (1994-06-01), None
patent: 8-181330 (1996-07-01), None
Nakatani Masaya
Yagi Yuji
Chapman John E.
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
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