Oxide Semiconductor Transistor Charge Management via Segmented Channel
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Solution Overview
Problem
In display devices using oxide semiconductors, unwanted charge build-up can lead to parasitic channels and leakage currents, particularly in the channel formation region of transistors, due to the wide band gap of oxide semiconductors, which affects the operation of driver circuits and pixel portions.
Innovation Solution
A display device structure incorporating depletion and enhancement type transistors with oxide semiconductor layers, where one transistor is used for discharging unwanted charge from signal lines and elements, reducing charge build-up and leakage currents by selectively turning on/off transistors to manage charge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If oxide semiconductor is used for channel formation layer, then field-effect mobility is improved and manufacturing process is simplified, but unwanted charge build-up occurs leading to parasitic channel and leakage current
Solution Approach 1:
The oxide semiconductor layer is divided into multiple regions with different thicknesses: a first region with greater thickness and a second region with smaller thickness. This segmentation allows different functional optimization - the thicker first region provides better charge storage capability to prevent parasitic channels, while the thinner second region maintains high field-effect mobility for efficient switching operation.
Solution Approach 2:
Different regions of the oxide semiconductor layer are given different local properties through varying thickness. The first region (thicker) is positioned to handle charge accumulation concerns, while the second region (thinner) is positioned where high mobility is critical for channel operation. This local differentiation resolves the contradiction between charge stability and mobility.
2Reliability
If oxide semiconductor is used for channel formation layer, then transistor off resistance is improved, but unwanted charge build-up is more likely to occur
Solution Approach 1:
The oxide semiconductor layer is segmented into a first region with greater thickness and a second region with smaller thickness. The thicker first region serves as a charge storage reservoir that can absorb unwanted charge build-up through controlled leakage, while maintaining the high off resistance of the oxide semiconductor material in the channel region.
Solution Approach 2:
The thicker first region acts as an intermediary between the channel formation region and the substrate, providing a controlled path for charge dissipation. This intermediary region prevents direct charge build-up in the channel while maintaining the insulating properties of oxide semiconductor, thus resolving the contradiction between high off resistance and charge accumulation.
3Object-generated harmful factors
If depletion type transistor is used for charge discharge, then charge build-up is reduced, but device complexity increases
Solution Approach 1:
The oxide semiconductor layer itself provides the charge management function through its inherent properties and结构设计. The multi-region thickness design enables the material to automatically regulate charge distribution - the thicker first region naturally accumulates and dissipates charge as needed, eliminating the requirement for additional depletion type transistors or complex charge management circuits.
Data Source
AI summary
A display device includes a driver circuit including a logic circuit including a first transistor which is a depletion type transistor and a second transistor which is an enhancement type transistor; a signal line which is electrically connected to the driver circuit; a pixel portion including a pixel whose display state is controlled by input of a signal including image data from the driver circuit through the signal line; a reference voltage line to which reference voltage is applied; and a third transistor which is a depletion type transistor and controls electrical connection between the signal line and the reference voltage line. The first to the third transistors each include an oxide semiconductor layer including a channel formation region.