The present invention relates to an improved acceleration measuring device, and more particularly to an acceleration measuring device which utilizes the cold cathode electron emission phenomenon.
Shown in FIG. 7 is a sectional view of a prior art semiconductor acceleration measuring device, hereinafter referred to as an accelerometer, manufactured by utilizing the micro-machining technique. This semiconductor accelerometer is described in Nikkei Mechanical, pp. 62-64 (December 1987), and the micro-machining technique utilized in the manufacture of this semiconductor accelerometer is described in Semiconductor World, pp. 62-64 (March 1992). This semiconductor accelerometer consists of a semiconductor chip 2 fixed inside a ceramics package 1 and immersed in silicone oil 1a.
The semiconductor chip 2 shown in FIG. 7 consists of a base disk portion 3, a sensor chip 4 connected to one end of the base disk portion 3, and a stopper portion 5 connected to the other end of the base disk portion 3. The sensor chip 4 consists of two thick end portions connected by a thin middle portion. One of the thick end portions of the sensor chip 4 is connected to the base disk portion 3, and a weight film 4b made of, for example, gold is deposited on top of the other thick portion, designated as 4a in FIG. 7, of the sensor chip 4. In addition, a plurality of independent semiconductor gauge layers which constitute a Wheatstone bridge circuit are formed on a major face of the sensor chip 4. A bonding wire is designated by the reference numeral 6.
When the semiconductor accelerometer is subject to acceleration, the thick portion 4a moves in response to inertial force. The plurality of semiconductor gauge layers are deformed as the thick portion 4a moves and generates a detection voltage indicative of the deformation (resistance variation) of the semiconductor gauge layers. By measuring the detection voltage, the magnitude and direction of the acceleration, i.e., the acceleration vector, are determined.
The above-described prior art semiconductor accelerometer is well suited for meeting small-size and mass production requirements. However, the above-described prior art semiconductor accelerometer has a major drawback: the prior art semiconductor accelerometer can not be used at high temperatures, i.e., above 150.degree. C. Further, since the characteristics of semiconductors change greatly with temperature variation even at temperature ranges well below 150.degree. C., the prior art semiconductor accelerometer cannot be practically used in most environments unless accompanied by a temperature compensation circuit. As a result of requiring a temperature compensation circuit, an operationally practical prior art semiconductor accelerometer is cumbersome to build and use.
It is an object of the present invention to provide an accelerometer which exhibits operational characteristics substantially independent of temperature variations in the environment.
It is another object of the present invention to provide an accelerometer which is well suited for mass production and meeting small-size requirements.