Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Tunneling through region of reduced conductivity
Reexamination Certificate
1999-11-22
2001-07-31
Mintel, William (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Tunneling through region of reduced conductivity
C257S021000, C257S025000, C257S290000, C257S291000, C438S066000, C438S073000, C438S096000
Reexamination Certificate
active
06268615
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to a photodetector which directly utilizes a gate current representative of the light intensity to obtain an optical signal about the information of image.
BACKGROUND OF THE INVENTION
Currently, the charge coupled device (CCD) is commonly used as an image detector and is widely applied in a scanner for scanning the plane pattern, a digital camera for recording the transient action, a video camera for recording sequential images, and a night vision equipment.
Because the charge packet stored in each storage cell (usually in a linear arrangement) of the CCD will be generated in response to the radiation of light and the magnitude of charge is directly proportional to the intensity of light, the readout signal in each storage cell must be processed by the successive steps to further obtain the information of the image. Moreover, the signal representative of the light intensity in each storage cell of the CCD must be outputted in a sequential manner, thereby reducing the signal-reading speed and decreasing the image recording rate. In addition, it also increases the complexity of rear circuits.
Thus, it is tried by the applicant to improve the above-described drawbacks of the CCD and to develop a preferred photodetector.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a photodetector adapted to be used with a voltage source for replacing the conventional CCD or photogate sensor. This photodetector directly utilizes a gate current representative of the light intensity to obtain an optical signal about the information of image and thus can be used as an ideal image detector.
The photodetector includes a semiconductor substrate electrically connected with an electrode of the voltage source for generating electron-hole pairs in response to a light, a conducting layer electrically connected with the other electrode of the voltage source, and an insulating layer formed between the conducting layer and the substrate, wherein one of electrons and holes, excited by the light, in the substrate will move to the conducting layer through the insulating layer so as to form a photo current when the voltage source provides a bias voltage.
The substrate can be a p-type or n-type silicon substrate. Preferably, the substrate is made of amorphous material such as amorphous Si:H.
Preferably, the insulating layer is a silicon oxide layer. The silicon oxide layer is formed by oxidizing the surface of the substrate through low-pressure rapid thermal oxidation. The rapid thermal oxidation is preferably performed at 1000° C. The insulating layer has a thickness of about several nanometers, which is thin enough to have a quantum mechanical tunneling of electrons or holes from the substrate to the conducting layer. For current VLSI chips, the useful bias voltage for generating the quantum mechanical tunneling effect ranges from 1.8 to 3.3 V.
Certainly, the conducting layer can be an aluminum layer, a doped polysilicon layer, or a transparent conductor. An example of transparent conductor is a transparent electrode made of indium tin oxide (ITO).
In accordance with one aspect of the present invention, the voltage source provides the bias voltage to generate a quantum tunneling effect such that the excited electrons/holes move to the conducting layer to form the photo current, an intensity of which is directly proportional to an intensity of the light. The photo current can be read out from the gate constituted by the conducting layer and then processed to obtain an optical signal The present invention may best be understood through the following description with reference to the accompanying drawings, in which:
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Lee Min-Hung
Lin I-Chen
Liu Cheewee
Klein & Szekeres LLP
Mintel William
National Science Council
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