Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Amorphous semiconductor material
Reexamination Certificate
2003-08-08
2004-09-07
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Amorphous semiconductor material
C257S415000, C257S417000, C257S421000, C257S522000, C257S618000, C257S735000, C257S723000, C257S418000, C257S419000, C257S414000, C257S420000
Reexamination Certificate
active
06787804
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to anacceleration sensor, and more specifically, to a semiconductor acceleration sensor with a low production cost and capable of avoiding generating leakage currents, thereby meeting market requirements.
2. Description of the Prior Art
An acceleration sensor is widely applied in seismology, automobilesafety air bag, robotics, and so on. Currently, anacceleration sensor in common use includes a piezoresistiveacceleration sensor, a piezoelectricacceleration sensor, a capacitiveacceleration sensor, and a semi-conductor acceleration sensor.
Additionally, because sizes of the acceleration sensors are reduced gradually, a micromachiningtechnology is developed to manufacture various microsensors and microactuators that are integrated with micro electronic circuits to form a microsystem, which is generally called a micro electro-mechanical system (MEMS). The MEMS has an extremely small size and can be manufactured by utilizing batch production for reducing a production cost. In addition, the MEMS and a signal processing circuit can be simultaneously formed on a silicon wafer for forming a monolithic device, which can reduce a distance between an acceleration sensor and the signal processing circuit and that is quite important for the acceleration sensor. As the acceleration sensor outputs a signal, the signal is firstly amplified by the signal processing circuit for preventing the signal from being disturbed by an ambient electromagnetic field, and the signal can be analog-to-digital(A/D) converted by the signal processing circuit and be transmitted to a central processing unit. Therefore, as the distance between the acceleration sensor and the signal processing circuit is reduced, signal reliability can be greatly improved, and interconnecting lines and loads of central control systems can be effectively decreased. As a result, the acceleration sensor that is manufactured by use of MEMS is developed rapidly due to its advantages of good detection sensitivity and a low production cost. Additionally, among the above-mentioned kinds of acceleration sensors, the piezoresistiveacceleration sensor has advantages of a high output voltage and high detection sensitivity, while the piezoelectricacceleration sensor has advantages of high detection sensitivity, a low electro-magnetic interruption, low power dissipation, high energy density, a fast response, and low sensitivity to an ambient environment. Accordingly, the piezoresistiveacceleration sensor and the piezoelectricacceleration sensor are usually applied on microsensors and microactuators in the MEMS field.
Please refer to FIG.
1
.
FIG. 1
is a sectional view of a conventional piezoresistive semiconductor acceleration sensor
10
. As shown in
FIG. 1
, the piezoresistive semiconductor acceleration sensor
10
comprises an etched semiconductor substrate
12
, such as a single-crystal silicon substrate or a silicon-on-insulator (SOI) substrate. The etched semiconductor substrate
12
includes a beam section
14
, an anchor section
16
for supporting the beam section
14
, and a weight section
18
positioned on an edge of the beam section
14
. Additionally, the piezoresistive semiconductor acceleration sensor
10
further comprisesat least one piezoresistor
20
located in the beam section
14
for being a sensing device of the piezoresistive semiconductor acceleration sensor
10
, and a control circuit
22
positioned in the etched semiconductor substrate
12
and electrically connected between the beam section
14
and the piezoresistor
20
. The control circuit
22
mainly includes a complementary metal-oxide semiconductor (CMOS), an amplifying circuit, or a logic circuit, and the control circuit
22
is used to receive, process, and transmit signals output from the piezoresistor
20
.
For forming the etched semiconductor substrate
12
, an anisotropic etching process is performed to etch a reverse side of a semiconductor substrate through use of an etchant, such as potassium hydroxide (KOH), so as to form the beam section
14
and the weight section
18
, whose areas and thickness conform to process requirements. Additionally, a portion of the beam section
14
is implanted with boron (B) through use of a thermal diffusing method or an ion implantation process for forming the piezoresistor
20
. Because the beam section
14
comprises single-crystal silicon, a p-n junction can be formed after the beam section
14
is implanted with boron (B), and the p-n junction forms the piezoresistor
20
that is used to measure a variation of pressure.
When a vertical acceleration force is applied on the piezoresistive semiconductor acceleration sensor
10
, a flexural vibration occurs in the piezoresistive semiconductor acceleration sensor
10
due to the much heavier weight section
18
. Because of the flexural vibration, the piezoresistor
20
is deformed and a resistance of the piezoresistor
20
is therefore altered. Thereafter, the control circuit
22
performs a signal process, such as signal amplification or temperature compensation, and the control circuit
22
converts a resistance variation of the piezoresistor
20
into a differential signal. Finally, the control circuit
22
outputs the differential signal. Therefore, the resistance variation of thepiezoresistor
20
that is directly proportional to the acceleration force can be measured, so that the acceleration force to be measured can be obtained.
Additionally, the semiconductor acceleration sensor
10
becomes a piezoelectric semiconductor acceleration sensor if the piezoresistor
20
is formed with a piezoelectric thin film, such as ZnO. The piezoelectric semiconductor acceleration sensoris driven according to the piezoelectric effect. As a vertical acceleration force is applied on the piezoelectric thin film, electric charges are generated at two ends of the piezoelectric thin film and the amount of the electric charges are directly proportional to the acceleration force. Accordingly, the acceleration force can be obtained through measuring a variation of the electric charges.
The conventional piezoresistive semiconductor acceleration sensorand the conventional piezoelectric semiconductor acceleration sensor are both composed of single crystal silicon, so that the conventional semiconductor acceleration sensor
10
has good detection sensitivity. However, a cost of single-crystal silicon is so high that it costs a lot to form the conventional semiconductor acceleration sensor
10
. Additionally, since the piezoresistor is formed through use of a thermal diffusing method or an ion implantation process in the prior art, the p-n junction is formed between the piezoresistor and the beam section of single-crystal silicon. Nevertheless, leakage currents are usually generated near the p-n junction, thus disturbing an operation of the sensor.
SUMMARY OF INVENTION
It is therefore a primary objective of the claimed invention to provide a semiconductor acceleration sensor with a low production cost and capable of reducing the abovementioned leakage currents.
According to the claimed invention, a semiconductor acceleration sensor is provided. The semiconductor acceleration sensor comprises a non-single-crystal-silicon-based substrate, an insulating beam structure having a movable section and a stationary section, at least one piezoresistor positioned on the beam structure, an insulating supporter positioned on the non-single-crystal-silicon-based substrate for fixing the stationary section of the beam structure and forming a distance between the beam structure and the non-single-crystal-silicon-based substrate, and a thin film transistor (TFT) control circuit positioned on the non-single-crystal-silicon-based substrate and electrically connected to the piezoresistor and the beam structure.
It is an advantage over the prior art that the semiconductor acceleration sensor of the claimed invention is formed on the non-single-crystal-silicon-based substrate, such as a glass substrate or other insulating substra
AU Optronics Corp.
Erdem Fazli
Hsu Winston
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