All-N-Channel Latch Circuit for Amorphous Silicon Displays
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Solution Overview
Problem
The fabrication of latch circuits using amorphous silicon TFTs is challenging due to their low mobility, making it difficult to create P-channel transistors, which are necessary for flat display apparatuses, and requiring separate processes for drive circuits using single-crystal silicon or polysilicon.
Innovation Solution
A clocked inverter circuit and latch circuit design that utilizes only N-channel transistors, where a series circuit with complementary clock-switching transistors is connected in series, with a first inverter circuit connected to the midpoint of the series circuit and a second inverter circuit receiving the output signal from the midpoint, allowing all transistors to be formed as N-channel transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If P-channel and N-channel transistors are used in latch circuits, then the circuit functionality is improved, but the manufacturing complexity increases due to requiring separate processes for single-crystal silicon or polysilicon
Solution Approach 1:
The patent applies homogeneity by using only N-channel transistors throughout the latch circuit, eliminating the need for P-channel transistors. This allows the entire circuit to be fabricated using a single transistor type and material system (amorphous silicon TFTs), thereby simplifying the manufacturing process while maintaining circuit functionality through the complementary clocked inverter configuration
Solution Approach 2:
The patent inverts the conventional approach by using N-channel transistors in configurations that traditionally required P-channel transistors. The complementary clocked inverter circuit uses N-channel transistors switched by complementary clock signals to achieve the same logical function, effectively replacing the standard P-channel/N-channel complementary structure with an all-N-channel implementation
2Ease of manufacture
If amorphous silicon TFTs are used, then the manufacturing process is simplified, but the transistor mobility decreases making P-channel transistor fabrication difficult
Solution Approach 1:
The patent uses homogeneity by consistently employing only N-channel transistors fabricated from amorphous silicon TFTs throughout the circuit. This eliminates the need to fabricate P-channel transistors, which are particularly difficult to create with amorphous silicon due to their inherently lower mobility. The uniform use of N-channel devices maximizes the advantage of the simplified amorphous silicon manufacturing process
Solution Approach 2:
The patent addresses the mobility limitation by changing the circuit design parameters - using complementary clocked inverters with carefully timed clock signals to control the N-channel transistors. This parameter change in the circuit topology compensates for the lower mobility of amorphous silicon TFTs compared to single-crystal or polysilicon transistors
3Reliability
If separate processes are used for drive circuits and pixel sections, then the circuit performance is improved, but the device complexity increases
Solution Approach 1:
The patent applies merging by integrating the drive circuit functionality directly into the same fabrication process as the pixel sections. By using only N-channel transistors that can be fabricated with amorphous silicon TFTs, the patent combines what were previously separate fabrication processes (one for drive circuits using single-crystal or polysilicon, another for pixel sections using amorphous silicon) into a single unified process, reducing device complexity while maintaining performance
Data Source
AI summary
The present invention is applied to flat display apparatuses using organic EL devices. Switching circuits implemented by a set of transistors TR1 and TR2 that perform on/off operations in a complementary manner form a series circuit, an output of the connection midpoint of the series circuit is output to an inverter circuit 33, an input signal IN is input to one end of the series circuit, and a signal that is output from an inverter circuit 34 and that corresponds to the output of the connection midpoint of the series circuit is supplied to an opposite end of the series circuit.