Highly sensitive photo-sensing element and photo-sensing device using the same

Abstract

According to the present invention, a highly sensitive photo-sensing element and a sensor driver circuit are prepared by planer process on an insulating substrate by using only polycrystalline material. Both the photo-sensing element and the sensor driver circuit are made of polycrystalline silicon film. As the photo-sensing element, a photo transistor is formed by using TFT, which comprises a first electrode 11 prepared on an insulating substrate 10 , a photoelectric conversion region 14 and a second electrode 12 , and a third electrode 13 disposed above the photoelectric conversion region 14 . An impurity layer positioned closer to an intrinsic layer (density of active impurities is 10 17 cm −3 or lower) is provided on the regions 15 and 16 on both sides under the third electrode 13 or on one of the regions 15 or 16 on one side.

1 . A photo-sensing element prepared on an insulating substrate, said photo-sensing element comprises a first electrode and a second electrode disposed by introducing highly-doped impurities on a first semiconductor layer, a photoelectric conversion region prepared by introducing an intrinsic layer or lowly-doped impurities on said first semiconductor layer is positioned between said first electrode and said second electrode, and a third electrode is arranged above said photoelectric conversion region via an insulating film. 
   
   
       2 . A photo-sensing element according to  claim 1 , wherein a third electrode is disposed via an insulating film above a partial region of said photoelectric conversion region except a region in contact with said first electrode and a region in contact with said second electrode. 
   
   
       3 . A photo-sensing element according to  claim 2 , wherein density of majority carriers in the semiconductor layer to form the first electrode and the second electrode is 1×10 19 /cm 3  or higher and density of majority carriers in the semiconductor layer to form the photoelectric conversion region is 1×10 17 /cm 3  or lower under the conditions with no light projected and with no voltage applied. 
   
   
       4 . A photo-sensing element according to  claim 3 , wherein density of majority carriers in the semiconductor layer to form a region in contact with the first electrode and a region in contact with the second electrode in the photoelectric conversion region is in the range from 1×10 17 /cm 3  to 1×10 19 /cm 3 . 
   
   
       5 . A photo-sensing element according to  claim 4 , wherein, when the sensor is in operation, the voltage on the second electrode is set to a value higher than the voltage on the first electrode, and the voltage applied on the third electrode is set to a value lower than the voltage on the first electrode. 
   
   
       6 . A photo-sensing element according to  claim 4 , wherein, when the sensor is in operation, the voltage applied on the second electrode is higher than the voltage applied on the first and the third electrodes. 
   
   
       7 . A photo-sensing element according to  claim 2 , wherein, when the first, the second and the third electrodes are projected vertically on the surface of the insulating substrate, each of a distance between the first electrode and the third electrode and a distance between the second electrode and the third electrode is 1 μm or more. 
   
   
       8 . A photo-sensing element according to  claim 1 , wherein a third electrode is disposed via an insulating film above a partial region of the photoelectric conversion region except a region in contact with the first electrode and a region in contact with the second electrode. 
   
   
       9 . A photo-sensing element according to  claim 8 , wherein, when the sensor is in operation, the voltage applied on the second electrode is higher than the voltage on the first electrode, and the voltage applied on the third electrode is lower than the voltage on the first electrode. 
   
   
       10 . A photo-sensing element according to  claim 8 , wherein, when the sensor is in operation, the voltage applied on the second electrode is higher than the voltage applied on the first electrode and the third electrode. 
   
   
       11 . A photo-sensing device, comprising a photo-sensing element provided on an insulating substrate and a photo-sensor driver processing circuit for processing the output from the photo-sensing element, wherein:
 said photo-sensing element comprises a first electrode and a second electrode prepared by introducing highly-doped impurities to a first semiconductor layer, there is provided a photoelectric conversion region prepared by introducing an intrinsic layer or lowly-doped impurities to said first semiconductor layer, and a third electrode is disposed above the photoelectric conversion region via an insulating film;   a switching element to constitute the photo-sensor driver processing circuit comprises a first electrode and a second electrode prepared by introducing highly-doped impurities to a first semiconductor layer, said switching element comprises an active layer region disposed between the first electrode and the second electrode on the first semiconductor layer, a third electrode is disposed via an insulating film above a partial region of the active layer region except a region in contact with the first electrode and the region in contact with the second electrode, said partial region is an intrinsic layer or a lowly-doped impurity layer, and, into the region in contact with the first electrode in the active layer region and into the region in contact with the second electrode, impurities are introduced in such quantity that the quantity of the impurities is fewer than the quantity of the impurities introduced into the first electrode and the second electrode and more than the quantity of the impurities introduced into the partial region.   
   
   
       12 . A photo-sensing device according to  claim 11 , wherein, under the conditions with no light projected and with no voltage applied, density of majority carriers in the semiconductor layer to form the first electrode and the second electrode of the photo-sensing element and the switching element is 1×10 19 /cm 3  or higher, density of majority carriers in the semiconductor layer to make up photoelectric conversion region of the photo-sensing element and partial region of the switching element is 1×10 17 /cm 3  or lower, and density of majority carriers in the semiconductor layer at two points to form the active layer region in contact with the first electrode and the second electrode of the switching element is in the range from 1×10 17 /cm 3  to 1×10 19 /cm 3 . 
   
   
       13 . A photo-sensing device according to  claim 12 , wherein density of majority carriers in the semiconductor layer to form photoelectric conversion region in contact with the first electrode or the second electrode of the photo-sensing element is in the range from 1×10 17 /cm 3  to 1×10 19 /cm 3 . 
   
   
       14 . An image display unit, comprising a photo-sensor disposed on an insulating substrate, a photo-sensor driver processing circuit for processing sensor signal from the photo-sensor, and a peripheral circuit for driving a plurality of pixels in response to the sensor signal, wherein:
 said photo-sensing element comprises a first electrode and a second electrode prepared by introducing highly-doped impurities to a first semiconductor layer, there is provided a photoelectric conversion region prepared by introducing an intrinsic layer or lowly-doped impurities to said first semiconductor layer, and a third electrode is disposed above the photoelectric conversion region via an insulating film;   a switching element to constitute the photo-sensor driver processing circuit comprises a first electrode and a second electrode prepared by introducing highly-doped impurities to a first semiconductor layer, said switching element comprises an active layer region disposed between the first electrode and the second electrode on the first semiconductor layer, a third electrode is disposed via an insulating film above a partial region of the active layer region except a region in contact with the first electrode and the region in contact with the second electrode, said partial region is an intrinsic layer or a lowly-doped impurity layer, and, into the region in contact with the first electrode in the active layer region and into the region in contact with the second electrode, impurities are introduced in such quantity that the quantity of the impurities is fewer than the quantity of the impurities introduced into the first electrode and the second electrode and more than the quantity of the impurities introduced into the partial region.   
   
   
       15 . An image display unit according to  claim 14 , wherein, under the conditions with no light projected and with no voltage applied, density of majority carriers in the semiconductor layer to form the first electrode and the second electrode of the photo-sensing element and the switching element is 1×10 19 /cm 3  or higher, density of majority carriers in the semiconductor layer to make up photoelectric conversion region of the photo-sensing element and partial region of the switching element is 1×10 17 /cm 3  or lower, and density of majority carriers in the semiconductor layer at two points to form the active layer region in contact with the first electrode and the second electrode of the switching element is in the range from 1×10 17 /cm 3  to 1×10 19 /cm 3 . 
   
   
       16 . An image display unit according to  claim 15 , wherein density of majority carriers in the semiconductor layer to form photoelectric conversion region in contact with the first electrode or the second electrode of the photo-sensing element is in the range from 1×10 17 /cm 3  to 1×10 19 /cm 3 .