Capacitive micro sensor, gyroscope, and input device

Details Capacitive micro sensor, gyroscope, and input device Capacitive micro sensor, gyroscope, and input device

2001-01-09

2003-03-25

Moller, Richard A. (Department: 2856)

Measuring and testing

Speed, velocity, or acceleration

Angular rate using gyroscopic or coriolis effect

Reexamination Certificate

active

06536281

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a capacitive micro sensor, a gyroscope, and an input device, specifically to a construction surrounding external pickup electrodes in the capacitive micro sensor.
2. Description of the Related Art
There has traditionally been a sensor that detects a dynamic magnitude of acceleration and pressure, etc., having a cantilever or a diaphragm in its structure. This type of sensor detects deformation of the cantilever or the diaphragm, produced when it receives an external force, as a variation of electrostatic capacity; and this detection method has generally been adopted.
FIG. 10
illustrates a capacitive acceleration sensor, as an example of this type of sensor.
A sensor shown in
FIG. 10
includes a silicon substrate
101
, and two glass substrates
102
,
103
, in which the silicon substrate is sandwiched between the two glass substrates. The silicon substrate
101
has an elastic portion
104
(cantilever), a weight
105
, and a conductive pole
106
, etc., formed therein. The weight
105
is supported at the front end of the elastic portion
104
so that the weight is able to displace to a force of inertia by acceleration. The glass substrates
102
,
103
have electrodes
107
,
108
formed thereon, in which the electrodes face to each other with minute gaps between the weight
105
and themselves. Thus, a variation of capacitances between the weight
105
and the electrodes
107
,
108
is detected as a detection signal. Both the glass substrates
102
,
103
and the silicon substrate
101
are hermetically connected by the anode junction method, however in order to secure the electric conductivity to the weight
105
and the electrodes
107
,
108
inside the sensor, the upper glass substrate
102
has holes
109
formed, and the holes
109
each have conductive layers
110
,
111
formed on the surfaces thereof, which are made of aluminum to ensure connections to the external circuits. The conductive layer
110
is electrically connected to the weight
105
through an impurity layer
112
, and the conductive layer
111
is electrically connected to the conductive pole
106
through an impurity layer
113
. Further, the conductive pole
106
is electrically connected to the electrodes
107
,
108
.
This type of sensor is achieved as a micro sensor using the micro-machining technique. In such a case, often the silicon substrate is used for the structural body of a cantilever or a diaphragm, etc., and the glass substrates are used for the supporting bodies that sandwich the silicon substrate. The reason is that the silicon substrate is a material that allows the micro fabrication using the semiconductor manufacturing technique, and the glass substrate is a material that can easily be joined with the silicon substrate by means of the anode junction method. Further, both the sides of the silicon substrate are sealed by the glass substrates, which will form a package for the sensor. When this construction is adopted, in order to achieve conductivity with the structural body and the electrodes made of silicon which are sealed inside the package, as mentioned above, the pick-up portions of electric signals are required which are referred to as the so-called field-through, such as the conductive layers formed on the holes that are perforated on the glass substrates, and the conductive pole formed with the silicon substrate.
However, the conventional capacitive micro sensor generates electric noise during outputting an electric signal as the detection signal to thereby deteriorate the S/N ratio and lower the detection sensitivity, which is a problem.
This is a serious problem especially in a type of sensor that vibrates a cantilever or a diaphragm before the external force is exerted thereto. The reason is that this type of sensor has a driving electrode for driving the cantilever or the diaphragm in addition to a detecting electrode. However, in the micro sensor, the driving electrode and the detecting electrode are formed adjacently with minute gaps in most cases, whereby the driving electrode and the detecting electrode are in a capacitive coupling. Accordingly, as the driving electrode has a drive signal supplied, being subject to the influence of the signal, the detecting electrode has undesired voltages induced and generates electric noise. Further, as in the foregoing example, when the detection signal is picked up by way of the feed-through, electric noise is generated in terms of the parasitic capacitance between the driving feed-through and the detecting feed-through.
As an example of a sensor provided with both the driving electrode and the detecting electrode, a gyroscope is known which uses a tuning fork made of a conductive silicon, and the like. This gyroscope detects a vibration perpendicular to the direction of the vibration, which is generated by the Coriolis' force when the legs of the tuning fork are vibrated (driven) in one direction and an angular velocity is inputted during the vibration with the longitudinal direction of the legs as the central axis. Because the magnitude of a vibration generated by the Coriolis' force corresponds to the magnitude of an angular velocity, the gyroscope can be applied to an angular velocity sensor, for example, to a coordinate input device for a personal computer, and so forth.
Although a great variety of contrivances have been made in regard to this gyroscope, still higher detection sensitivity thereof is desired. To realize further enhancement of the detection sensitivity, the problem of the foregoing electric noise must be solved in the gyroscope as well. Also, in view of the current situations of further miniaturization in various sensors, the generation of electric noise by the capacitive coupling between driving electrodes, or between detecting electrodes is considered as ignorable.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing problem, and provides a capacitive micro sensor, a gyroscope, and an input device using the gyroscope, capable of suppressing to the utmost the electric noise generated around the electrodes inside the sensor and enhancing the detection sensitivity by an enhanced S/N ratio.
In accordance with an aspect of the invention, the capacitive micro sensor includes a structural body, at least one driving electrode that drives the structural body, at least one driving line portion that supplies the driving electrode with a drive signal, at least one detecting electrode that detects a displacement of the structural body driven by the driving electrode on the basis of a variation of capacitance, and at least one detecting line portion that transmits a detection signal from the detecting electrode, wherein a shield member is provided between the driving electrode and the detecting electrode, or between the driving line portion and the detecting line portion, that makes electrostatic shielding between the electrodes or between the line portions.
In accordance with an aspect of the invention, the gyroscope includes a vibratory strip, a driving electrode disposed to face to the vibratory strip, that drives the vibratory strip, a driving line portion that supplies the driving electrode with a drive signal, a detecting electrode disposed facing to the vibratory strip, that detects a displacement perpendicular to the drive direction of the vibratory strip, and a detecting line portion that transmits a detection signal from the detecting electrode, where a first shield member is provided between the driving electrode and the detecting electrode, or between the driving line portion and the detecting line portion, that makes electrostatic shielding between the electrodes or between the line portions.
In this invention, the “line portion” when referred to as the “driving line portion” or the “detecting line portion” signifies the whole portion serving as the transmission paths electrically connected to the driving electrode, detecting electrode, and the like, that exchanges signals be

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