Asymmetric Source Electrode Overhang for InGaZnO TFT Rear Surface Current Suppression
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Solution Overview
Problem
InGaZnO thin-film transistors (TFTs) face issues with rear surface currents due to the accumulation layer channel structure, leading to degradation of sub-threshold swing, increased off current, and poor 1/f noise characteristics, especially when operated near threshold voltage with a small gate electric field.
Innovation Solution
The semiconductor device configuration includes a gate electrode, first and second dielectric films, and asymmetrically formed source and drain electrodes, where the source wiring portion overhangs towards the drain wiring portion, effectively inhibiting rear surface currents by acting as a back gate and increasing the threshold voltage, thereby reducing off leak current and improving 1/f noise characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the channel length becomes shorter with increasingly finer patterns, then the transistor size is reduced and integration density is improved, but rear surface current flows through both the channel region near the gate dielectric film interface and near the interface with the dielectric film on the rear surface, causing degradation of device performance
Solution Approach 1:
The patent applies asymmetry by forming the source electrode to overhang the drain electrode in the channel width direction. This asymmetric configuration creates an electric field distribution that suppresses rear surface current formation while maintaining short channel dimensions for high integration density.
Solution Approach 2:
The patent implements preliminary anti-action by pre-configuring the source electrode overhang structure before device operation. This pre-configuration creates a preliminary electric field that counteracts the formation of rear surface current paths, preventing the harmful effect before it occurs during transistor operation.
2Use of energy by moving object
If the InGaZnO-TFT is operated near a threshold voltage where the gate electric field is small, then power consumption is reduced, but rear surface current becomes difficult to control by the gate electrode, causing degradation of sub-threshold swing and increase of off current
Solution Approach 1:
The asymmetric source electrode configuration creates a non-uniform electric field distribution that enhances gate control over the channel, including the rear surface region. This improved control maintains effective sub-threshold swing even when operating at low gate electric fields for reduced power consumption.
Solution Approach 2:
The patent applies local quality by creating different electric field conditions in different regions of the channel. The source electrode overhang generates a localized electric field enhancement near the source region that improves carrier injection control, while maintaining low overall gate electric field for power efficiency.
3Reliability
If the source electrode is formed to overhang the drain electrode, then rear surface current is suppressed and threshold voltage is increased, but the device structure becomes more complex
Solution Approach 1:
The patent merges the source electrode function with an additional capability by extending it to overhang the drain electrode. This single structural modification simultaneously achieves rear surface current suppression and threshold voltage control without requiring separate additional components, thereby limiting the increase in device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly reduces rear surface currents, enhances sub-threshold swing, and improves 1/f noise characteristics by effectively controlling the channel region and increasing the threshold voltage, leading to improved device performance.
Implementation Method 1
the source wiring portion overhangs towards a center direction of the oxide semiconductor film on a source electrode side more than on a drain electrode side... effectively inhibiting rear surface currents by acting as a back gate
Data Source
AI summary
A semiconductor device according to an embodiment, includes a first dielectric film arranged above a gate electrode, an oxide semiconductor film arranged above the first dielectric film, a second dielectric film arranged above the oxide semiconductor film, a drain electrode having a drain contact portion that is arranged in the second dielectric film and connects one end side of the oxide semiconductor film to a wire of an upper layer, and a source electrode having a source contact portion that is arranged in the second dielectric film and connects another end side of the oxide semiconductor film to a wire of an upper layer. A wiring portion arranged above the second dielectric film and forming the wire of the upper layer is formed to overhang toward a center direction of the oxide semiconductor film on a source electrode side more than on a drain electrode side.