Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
1999-02-11
2001-06-05
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C073S514180, C361S280000
Reexamination Certificate
active
06240782
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims priority from Japanese Patent Applications No. Hei. 10-30045 filed Feb. 12, 1998 and No. Hei. 10-367421 filed Dec. 24, 1998, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor physical quantity sensor, having a beam-structure movable portion and a fixed portion, for measuring a physical quantity, such as acceleration, yaw rate or vibration by detecting a capacitance change between the beam-structure movable portion and the fixed portion, and a method of producing such a sensor.
2. Description of Related Art
A conventional semiconductor physical quantity sensor having a beam-structure movable portion is a known differential servo-control capacitance acceleration sensor employing an attached substrate unit (as disclosed in Japanese Patent Application Laid-open No. Hei. 9-211022).
This sensor, formed from a beam-structure movable portion and a fixed portion on a substrate (support substrate), detects a physical quantity by detecting a capacitance change between the beam-structure movable portion and the fixed portion. The beam-structure has a first anchor and a mass portion supported by the anchor via a beam portion. This mass portion has a movable electrode that moves upon application of a force caused by acceleration. The fixed portion has a fixed electrode facing the movable electrode and fixed to the substrate by a second anchor. Further, the substrate has an attaching thin film formed on a semiconductor substrate, an insulating film formed on the attaching thin film and a conductive film formed on the insulating film. The first and second anchor portions are formed from a conductive film.
In this acceleration sensor, sensitivity of the sensor is largely affected by parasitic capacitance formed between the conductive film and the insulating film or the attaching thin film. Specifically, when a capacitance between the beam-structure and fixed portion is measured, sensor output is represented by (capacitance variation)/((total capacitance)+(parasitic capacitance)). Therefore, when the attaching film is electrically floated, the parasitic capacitance is, and the sensitivity of the sensor is small.
In general, the above semiconductor physical quantity sensor is produced by employing a semiconductor producing method such as etching, so that a separation trench separating the movable portion from the fixed portion is formed in an element forming film formed on the support substrate. Therefore, at a surrounding portion of a sensor element portion having the movable portion and the fixed portion, there is an element forming film portion that is another portion of the sensor element portion.
Furthermore, although the surrounding portion is supported by the support substrate, this portion is electrically floated. This structure leads to change the sensor output as in the attaching thin film structure.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide a semiconductor physical quantity sensor which can prevent a decrease in sensitivity caused by the parasitic capacitance of the attaching thin film.
A second object of the present invention is to provide a semiconductor physical quantity sensor which can prevent a decrease in sensitivity caused by the parasitic capacitance formed in the surrounding portion of a sensor element portion.
According to one aspect of the present invention, a semiconductor physical quantity sensor comprises: a sensor element portion, a surrounding portion provided at a surrounding region of the sensor element portion and insulated from the sensor element portions and potential fixing means for fixing a potential of the surrounding portion.
This structure enables the potential of the surrounding portion to be fixed, so that parasitic capacitance can be decreased. Therefore, it can prevent a decrease in sensitivity caused by the parasitic capacitance of the surrounding portion.
According to one aspect of the present invention, a semiconductor physical quantity sensor comprises: a substrate having a first conductive film, an insulating film and a second conductive film, each being laminated on a semiconductor substrate; a beam-structure having a movable electrode, supported on a surface of the substrate by a first anchor, the first anchor being formed from the second conductive film; a fixed electrode faced to the movable electrode, fixed to the surface of the substrate by a second anchor, the second anchor being formed from the second conductive film; and film potential fixing means for fixing a potential of the first conductive film.
This structure enables the potential of the first conductive film to be fixed, so that parasitic capacitance can be decreased. Therefore, it can prevent sensing sensitivity from decreasing caused by the parasitic capacitance of the first conductive film from decreasing.
According to another aspect of the present invention, a semiconductor physical quantity sensor comprises: a substrate having a support substrate and an element forming film formed on the support substrate; a sensor element portion formed on the substrate having a movable portion, the sensor element portion detecting a capacitance change in response to a movement of the movable portion; a surrounding portion provided at a surrounding region of the sensor element portion and divided from the sensor element portion with a trench formed in the element forming film; and region potential fixing means for fixing a potential of the surrounding portion.
This structure enables the potential of the surrounding portion to be fixed, so that parasitic capacitance can be decreased. Therefore, it can prevent sensing sensitivity from decreasing caused by the parasitic capacitance of the surrounding portion.
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Fukada Tsuyoshi
Kato Nobuyuki
Sakai Minekazu
Yamamoto Toshimasa
Denso Corporation
Kwok Helen
Pillsbury & Winthrop LLP
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