Staggered Oxide TFT Buffer Layer Contact Resistance
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Solution Overview
Problem
Thin film transistors with oxide semiconductor films face challenges in achieving high-speed operation and reliability due to increased contact resistance and capacitance, particularly in large-area display devices, which affects signal delay and display uniformity.
Innovation Solution
A staggered thin film transistor structure is implemented with an oxide semiconductor film containing indium, gallium, and zinc, using a buffer layer with higher carrier concentration than the semiconductor layer to reduce contact resistance and parasitic capacitance, and optimizing the carrier concentration range to prevent the transistor from becoming normally on.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a low resistance metal material is used for source and drain electrodes to reduce signal delay, then electrical conductivity is improved, but contact resistance increases due to Schottky junction formation
Solution Approach 1:
An oxide semiconductor buffer layer is introduced as an intermediary between the low-resistance metal electrode and the oxide semiconductor film. This buffer layer has higher carrier concentration than the main semiconductor film, enabling ohmic contact while maintaining the low resistance properties of the metal electrode. The buffer layer acts as a mediator that prevents Schottky junction formation at the electrode-semiconductor interface.
Solution Approach 2:
The oxide semiconductor buffer layer is selectively formed only in the contact regions between the source/drain electrodes and the semiconductor film, while the channel region maintains its original lower carrier concentration. This local differentiation allows the contact regions to have high conductivity (reducing signal delay) while the channel region maintains proper transistor characteristics.
2Device complexity
If source and drain electrodes are in direct contact with oxide semiconductor film to reduce manufacturing complexity, then device structure is simplified, but parasitic capacitance increases hindering high speed operation
Solution Approach 1:
The oxide semiconductor buffer layer serves as a mediator between the electrode and the main semiconductor film. By controlling the thickness and carrier concentration of this buffer layer, parasitic capacitance is reduced while maintaining electrical connectivity. The buffer layer's higher carrier concentration creates a depletion region that minimizes capacitive coupling between the electrode and the channel-forming semiconductor film.
3Reliability
If oxide semiconductor film with high carrier concentration is used to reduce contact resistance, then electrical conductivity is improved, but transistor becomes normally on state
Solution Approach 1:
The oxide semiconductor structure is differentiated into two regions with different carrier concentrations: a buffer layer with high carrier concentration (1×10^19 to 1×10^21 cm^-3) at the electrode contact regions for low contact resistance, and a main semiconductor film with lower carrier concentration (1×10^16 to 1×10^18 cm^-3) in the channel region for proper transistor switching control. This spatial differentiation of electrical properties resolves the contradiction between contact resistance and transistor controllability.
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 approach results in a thin film transistor with reduced contact resistance, improved frequency characteristics, and enhanced reliability, enabling high-speed and reliable operation with reduced variation in electric properties and display uniformity.
Implementation Method 1
a buffer layer which has a higher carrier concentration than the semiconductor layer is used, contact resistance can be reduced
Implementation Method 2
capacitance is formed in a portion where the source and drain electrodes and the oxide semiconductor film have a direct contact with each other, and there are risks that frequency characteristics (called 'f characteristics') decrease
Data Source
AI summary
An embodiment is to include a staggered (top gate structure) thin film transistor in which an oxide semiconductor film containing In, Ga, and Zn is used as a semiconductor layer and a buffer layer is provided between the semiconductor layer and a source and drain electrode layers. The buffer layer having higher carrier concentration than the semiconductor layer is provided intentionally between the source and drain electrode layers and the semiconductor layer, whereby an ohmic contact is formed.