Active matrix device with photo sensor
View Patent ↗An active matrix pixel device is provided, for example an electroluminescent display device, the device comprising circuitry supported by a substrate and including a polysilicon TFT ( 10 ) and an amorphous silicon thin film PIN diode ( 12 ). Polysilicon islands are formed before an amorphous silicon layer is deposited for the PIN diode. This avoids the exposure of the amorphous silicon to high temperature processing. The TFT comprises doped source/drain regions ( 16 a , 17 a ), one of which ( 17 a ) may also provide the n-type or p-type doped region for the diode. Advantageously, the requirement to provide a separate doped region for the photodiode is removed, thereby saving processing costs. A second TFT ( 10 b ) having a doped source/drain region ( 16 b , 17 b ) of the opposite conductivity type may provide the other doped region ( 16 b ) for the diode, wherein the intrinsic region ( 25 ) is disposed laterally between the two TFTs, overlying each of the respective polysilicon islands.
1. A method of manufacturing an active matrix pixel device comprising a thin film transistor which includes a polycrystalline silicon channel and doped source/drain regions, and a PIN diode which includes a p-type doped region and an n-type doped region separated by an amorphous silicon intrinsic region, the method including:
(a) - forming a plurality of polycrystalline silicon islands on a substrate, one of which providing a transistor channel, and source/drain regions; and then,
(b) - depositing and patterning a layer of amorphous silicon to provide the amorphous silicon intrinsic region of the PIN diode such that the intrinsic region overlies and contacts at least a part of one of the polycrystalline silicon islands which provides one of the p-type or n-type doped regions.
2. A method according to claim 1 , wherein the source/drain regions and said one of the p-type or n-type doped regions of the PIN diode are provided by the same polycrystalline silicon island.
3. A method according to claim 1 , wherein the source/drain regions are doped n-type, and wherein the method further comprises:
(c) - depositing and patterning a layer of aluminium to define a top PIN diode contact on the intrinsic region of the PIN diode;
(d) - annealing the top PIN diode contact to cause aluminium ions to diffuse into the underlying intrinsic region to form the p-type doped region.
4. A method according to claim 3 , further comprising:
(e) - etching away part of the top PIN diode contact so as to expose the PIN diode to input light.