Oxide Channel Layer Crystallinity for Light Stability
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Solution Overview
Problem
Oxide semiconductor films, such as IGZO, used in thin film transistors exhibit instability due to changes in electrical characteristics when exposed to light, causing shifts in threshold voltage.
Innovation Solution
An active device structure with a gate, oxide channel layer, source, and drain, where the oxide channel layer is divided into top and bottom layers with different crystalline structures, and a high power deposited insulation layer contacts the top layer, which is fabricated using a method involving high power deposition and annealing to stabilize the device against light-induced carrier transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an oxide semiconductor film is used to form the channel layer of a thin film transistor, then the device can be fabricated with the oxide material properties, but the electrical characteristics of the oxide semiconductor film change after exposure to light irradiation causing threshold voltage shifts
Solution Approach 1:
The oxide channel layer is divided into multiple layers with different crystalline structures. The first layer has a first crystalline structure and the second layer has a second crystalline structure different from the first. This segmentation allows each layer to contribute different properties, with the crystalline structure providing stability against light-induced threshold voltage shifts while maintaining manufacturability
Solution Approach 2:
Different regions of the oxide channel layer are given different crystalline structures. The first layer and second layer have distinct local crystalline properties, where the crystalline structure in at least one layer provides resistance to light-induced carrier transitions, thereby stabilizing the threshold voltage while preserving the overall device functionality
2Use of energy by moving object
If the oxide semiconductor film is exposed to light irradiation, then carriers transition to the conduction band, but this causes instability in the threshold voltage of the thin film transistor
Solution Approach 1:
The crystalline structure parameter of the oxide channel layer is changed and controlled to create specific stable phases. By forming layers with defined crystalline structures, the material's response to light irradiation is modified, preventing unwanted carrier transitions to the conduction band and stabilizing the threshold voltage while allowing necessary electrical operation
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
The structure effectively blocks light-induced carrier transitions, preventing early jumps to the conduction band and reducing threshold voltage shifts, thereby enhancing the stability of the active device.
Implementation Method 1
the top layer can function to provide the effect of blocking light
Implementation Method 2
an annealing step is performed for the oxide channel layer including the bottom layer and the top layer which contact with the high power deposited insulation layer
Implementation Method 3
the crystalline structure of the top layer is different from the crystalline structure of the bottom layer
Data Source
AI summary
An active device structure and a method of fabricating an active device are provided. The active device structure includes a gate, an oxide channel layer, a source, a drain and a high power deposited insulation layer. The gate and the oxide channel layer are overlapped in a top and bottom manner. The oxide channel layer includes a top layer and a bottom layer having a crystalline structure different from a crystalline structure of the top layer. The source and the drain both contact the oxide channel layer, wherein a gap separating the source and the drain defines a channel area. The high power deposited insulation layer contacts the top layer of the oxide channel layer. The top layer of the oxide channel layer provides the effect of blocking light, which solves the problem of threshold voltage shift due to the light irradiation on the oxide channel layer.