Abstract:
An image sensor includes a light-sensing element, a first transistor, and a second transistor. The light-sensing element has a first end and a second end electrically connected to a select line. The first transistor has a first end electrically connected to a first control line, a control end electrically connected to the first end, and a second end electrically connected to the first end of the light-sensing element. The second transistor has a first end electrically connected to a voltage source, a control end electrically connected to the first end of the light-sensing element, and a second end electrically connected to an output line. The light-sensing element uses the material of silicon rich oxide so that the light-sensing element can sense the luminance variance and have the characteristic of the capacitor for the level boost.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. application Ser. No. 12/561,277 filed Sep. 17, 2009, the entire contents of which are included herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to an image sensor, and more particularly, to an image sensor formed by the silicon rich oxide material. 
     2. Description of the Prior Art 
     The conventional image sensor utilizes the built-in amplifier component of each pixel to amplify the photoelectric conversion signal. Each pixel then utilizes the XY addressing method to select for obtaining the voltage level of the photoelectric conversion signal. Since each pixel includes the built-in amplifier component, the photoelectric component (i.e. the light sensing component) generates the sensing signal of photo charges when beamed with light, and the sensing signal is amplified by the built-in amplifier component accordingly. This way, the sensing signal is not easily affected by the noise when being transmitted from the photoelectric component to the external control circuit. From the circuit design&#39;s point of view, the sensitivity of the image sensor is dependent on three main factors. The first factor is the area of the light sensing component. Fundamentally, the area of the light sensing component is directly proportional to the intensity of the sensed photo charges under identical luminance; increasing the area of the light sensing component increases the photo charges generated by the light sensing component. The second factor is the capacitance of the integrating capacitor. Theoretically, under the same stored electrical charge, the voltage at the two ends of the capacitor is inversely proportional to the capacitance; increasing the capacitance decreases the voltage at the two ends of the capacitor. The third factor is the gain of the sensing amplifier of the light sensing component. 
     SUMMARY OF THE INVENTION 
     The present invention discloses an image sensor. The image sensor comprises a light sensing component, a first transistor and a second transistor. The light sensing component has a first end, and a second end electrically connected to a select line. The first transistor has a first end electrically connected to a first control line, a control end electrically connected to the first end, and a second end electrically connected to the first end of the light sensing component. The second transistor has a first end electrically connected to a voltage source, a control end electrically connected to the first end of the light sensing component, and a second end electrically connected to an output line. 
     The present invention further discloses an image sensor. The image sensor comprises a light sensing component, a diode and a source follower. The light sensing component has a first end, and a second end electrically connected to a select line. The diode has a first end electrically connected to a control line, and a second end electrically connected to the first end of the light sensing component. The source follower has an input end electrically connected to the first end of the light sensing component, and an output end electrically connected to an output line, for outputting a sensing voltage generated by the light sensing component. 
     The present invention further discloses a method for detecting the luminance variation by using an image sensor, the image sensor comprising a light sensing component having a first end and a second end electrically connected to a select line; a first transistor having a first end electrically connected to a control line, a control end electrically connected to the first end and a second end electrically connected to the first end of the light sensing component; and a second transistor having a first end electrically connected to a voltage source, a control end electrically connected to the first end of the light sensing component and a second end electrically connected to an output line. The method comprises the control line transmitting a high level voltage to turn on the first transistor, for resetting a voltage level of the light sensing component; the control line transmitting a low level voltage to turn off the first transistor, for the light sensing component to generate a voltage drop when sensing light; and the select line transmitting the high level voltage for transmitting the voltage drop to the output line via the second transistor. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram illustrating the image sensor according to the first embodiment of the present invention. 
         FIG. 2  is a waveform diagram illustrating the operation sequence of the image sensor of the present invention. 
         FIG. 3  is a diagram illustrating the cross-section view of the image sensor of the present invention. 
         FIG. 4  is a diagram illustrating the image sensor according to the second embodiment of the present invention. 
         FIG. 5  is a diagram illustrating the image sensor according to the third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1 .  FIG. 1  is a circuit diagram illustrating the image sensor  30  according to the first embodiment of the present invention. The light sensor  30  comprises a first transistor  21 , a light sensing component  22 , a second transistor  24  and a reference current source  25 . In the present invention, the light sensing component  22  can be realized with a capacitor formed by a metal layer, a silicon rich oxide layer and a transparent metal layer, wherein the transparent metal layer can be made of Indium Tin Oxide (ITO). One end of the light sensing component  22  is electrically connected to the row select line S 2  and the other end of the light sensing component  22  is electrically connected to the source electrode of the first transistor  21  and the gate electrode of the second transistor  24 . The gate electrode and the source electrode of the first transistor  21  are electrically connected to form a diode component which is controlled by the reset signal line S 1 . The drain electrode of the second transistor  24  is electrically connected to the voltage source VDD; the gate electrode of the second transistor  24  is electrically connected to the light sensing component  22  and the source electrode of the transistor  21 , forming a source follower which functions as the capacitance-voltage amplifier; the source electrode of the second transistor  24  is electrically connected to the column output line S 3 . The reference current source  25  is electrically connected to the column output line S 3 , the reference current source  25  provides the output current according to a reference voltage VREF. 
     Please refer to  FIG. 2 .  FIG. 2  is a waveform diagram illustrating the operation sequence of the image sensor  30  of the present invention. The operation sequence of the image sensor  30  can be roughly categorized into the reset phase T 0 , the integration phase T 1  and the reading phase T 2 . The operation sequence of the image sensor  30  is explained as below: 
     Step 1: When the reset signal S 1  is at the low voltage level (VSS), the voltage level of the node A 3  of the light sensing component  22  is floating. When the reset signal S 1  is converted from the low voltage level (VSS) to the high voltage level (VREF), the image sensor  30  enters the reset phase T 0 , and the diode component formed by the first transistor  21  is turned on due to the component operating in forward bias. When the reset signal line S 1  is at the high voltage level (VREF), the node A 3  of the light sensing component  22  is charged to the voltage level of (VREF−Vth) since the diode component is operating in forward bias, wherein Vth represents the threshold voltage of the first transistor  21 . 
     Step 2: When the reset signal S 1  is converted from the high voltage level (VREF) to the low voltage level (VSS), the diode component formed by the first transistor  21  is turned off due to the component operating in reverse bias. At the moment the voltage drop between the two ends of the light sensing component  22  is (VREF−Vth)−VSS, and the voltage level of the node A 3  of the light sensing component  22  is floating; the image sensor  30  enters the integration phase T 1 . 
     Step 3: when the image sensor  30  is in the integration phase T 1 , the voltage level of the node A 3  of the light sensing component  22  varies according to the luminance of the incident light. When the light sensing component  22  is beamed with light, the node A 3  of the light sensing component  22  generates photo charges. The generated photo charges neutralize the stored charges of the node A 3  of the light sensing component  22 , diminishing the voltage drop between the two ends of the light sensing component  22 . The higher the luminance of the incident light, the lower the voltage level of the node A 3  of the light sensing component  22 . For instances, when the light luminance B is greater than the light luminance A (i.e. Lux B&gt;Lux A), the gradient of the decreasing rate of the voltage level of the node A 3  for the light luminance A is also greater than that of the light luminance B (i.e. mB&gt;mA) 
     Step 4: Since the diode component of the first transistor  21  is turned off due to the component operating in reverse bias, the voltage level of the node A 3  of the light sensing component  22  is still floating. When the row select line S 2  is converted from the low voltage level (VSS) to the high voltage level (VREF), the voltage level of the node A 3  increases by (VREF−VSS) accordingly, as the voltage drop between the two ends of the light sensing component  22  (with characteristics of a capacitor) does not change instantaneously. 
     Step 5: When the voltage level of the node A 3  of the light sensing component  22  has increased by (VREF−VSS) due to the light sensing component  22  with the characteristics of the capacitor, the voltage level of the node A 3  is sufficient to turn on the second transistor  24  of the source follower. 
     Step 6: When the second transistor  24  of the source follower is turned on, the signal (equivalent to the voltage level of the node A 4 ) of the column output line S 3  is equivalent to the increased voltage level of the node A 3  of the light sensing component  22  subtracting the threshold voltage Vth of the second transistor  24 . For instances, the signal of the column output line S 3  is (VA−Vth) for the light luminance Lux A and (VB−Vth) for the light luminance Lux B. 
     Please refer to  FIG. 3 .  FIG. 3  is a diagram illustrating the cross-section view of the image sensor  30  of the present invention. A first transistor  21  and a second transistor  24  are formed on the substrate  31 . A gate oxide layer  32 , a first insulation layer  33  and a second insulation layer  34  are formed between the first transistor  21 , the second transistor  24  and the light sensing component  22 . The first transistor  21  is an N-type Metal Oxide Semiconductor (NMOS) transistor, comprises a gate electrode  211 , a source electrode  212  and a drain electrode  213 . The second transistor  24  is an NMOS transistor, comprises a gate electrode  241 , a source electrode  242  and a drain electrode  243 . The light sensing component  22  comprises a metal layer  221 , a silicon rich oxide layer  222  and a transparent metal layer  223 . 
     Please refer to  FIG. 4 .  FIG. 4  is a diagram illustrating the image sensor  50  according to the second embodiment of the present invention. The image sensor comprises a first transistor  51 , a light sensing component  52 , a second transistor  54  and a third transistor  55 . In the second embodiment, the third transistor  55  is utilized to replace the reference current source  25 . The row output line S 3  is electrically connected to the drain electrode of the third transistor  55 ; the gate electrode of the third transistor  55  is controlled by the signal line Vb; the source electrode of the third transistor  55  is electrically connected to the reference voltage source VREF. 
     Please refer to  FIG. 5 .  FIG. 5  is a diagram illustrating the image sensor  60  according to the third embodiment of the present invention. The image sensor  60  comprises a diode  61 , a light sensing component  62 , a second transistor  64 , a sampling capacitor  65  and a third transistor  66 . In the third embodiment, the sampling capacitor  65  and the third transistor  66  are utilized to replace the reference current source  25 . In addition, the diode  61  also replaces the first transistor  21 . The row output line S 3  is electrically connected to the drain electrode of the third transistor  65  and one end of the sampling capacitor  65 ; the gate electrode of the third transistor  65  is controlled by the signal line REST 2 ; the source electrode of the third transistor  65  is electrically connected to the other end of the sampling capacitor  65  and the reference voltage source VREF. 
     In conclusion, the image sensor of the present invention comprises a light sensing component, a first transistor and a second transistor. The light sensing component comprises a first end and a second end electrically connected to a select line. The first transistor comprises a first end electrically connected to a first control line, a control end electrically connected to the first end, and a second end electrically connected to the first end of the light sensing component. The second transistor comprises a first end electrically connected to a voltage source, a control end electrically connected to the first end of the light sensing component, and a second end electrically connected to an output line. The light sensing component is made of silicon rich oxide material, so the light sensing component is able to detect the variation of the light luminance. At the same time, the light sensing component possesses the characteristics of the integrating capacitor, and can be utilized for increasing the corresponding voltage level. Therefore, the image sensor of the present invention utilizes two transistors and the light sensing component made of the silicon rich oxide material, for simplifying the circuit structure. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.