Pixel current driver for organic light emitting diode displays

Abstract

A pixel current driver comprises a plurality of thin film transistors (TFTs) each having dual gates and for driving OLED layers. A top gate of the dual gates is formed between a source and a drain of each of the thin film transistors, to thereby minimize parasitic capacitance. The top gate is grounded or electrically tied to a bottom gate. The plurality of thin film transistors may be two thin film transistors formed in voltage-programmed manner or five thin film transistors formed in a current-programmed ΔV T -compensated manner. Other versions of the current-programmed circuit with different numbers of thin film transistors are also presented that compensate for δV T . The OLED layer are continuous and vertically stacked on the plurality of thin film transistors to provide an aperture ratio close to 100%.

We claim:  
     
         1 . A pixel current driver for an organic light emitting diode (OLED) having an OLED layer for emitting light, comprising: 
 a plurality of thin film transistors (TFTs) each having dual gates and for driving the OLED layer, a top gate of the dual gates being formed between a source and a drain of each of the thin film transistors, to thereby minimize parasitic capacitance.    
     
     
         2 . The pixel current driver as claimed in  claim 1 , wherein each of the thin film transistor is an a-Si:H based thin film transistor.  
     
     
         3 . The pixel current driver as claimed in  claim 1 , wherein each of the thin film transistor is a polysilicon-based thin film transistor.  
     
     
         4 . The pixel current driver as claimed in  claim 3 , wherein each of the thin film transistors is a p-channel thin film transistor.  
     
     
         5 . The pixel current driver as claimed in  claim 2 , wherein the dual gates are fabricated in a normal inverted staggered TFT structure.  
     
     
         6 . The pixel current driver as claimed in  claim 2 , wherein the top gate is grounded.  
     
     
         7 . The pixel current driver as claimed in  claim 2 , wherein the top gate is electrically tied to a bottom gate.  
     
     
         8 . The pixel current driver as claimed in  claim 2 , wherein the plurality of thin film transistors are two thin film transistors.  
     
     
         9 . The pixel current driver as claimed in  claim 8 , wherein the two thin film transistors are formed in a voltage programmed manner.  
     
     
         10 . The pixel current driver as claimed in  claim 2 , wherein the plurality of thin film transistors are five thin film transistors.  
     
     
         11 . The pixel current driver as claimed in  claim 10 , wherein the five thin film transistors are formed in a current-programmed ΔV T -compensated manner.  
     
     
         12 . The pixel current driver as claimed in  claim 2 , wherein the OLED layer is continuously and vertically stacked on the plurality of thin film transistors.  
     
     
         13 . The pixel current driver as claimed in  claim 2 , wherein the pixel current driver is a current mirror based pixel current driver for automatically compensating for shifts in the Vth of each of the thin film transistor in a pixel.  
     
     
         14 . The pixel current driver as claimed in  claim 10 , wherein the pixel current driver is for monochrome displays.  
     
     
         15 . The pixel current driver as claimed in  claim 10 , wherein the pixel current driver is for full color displays.