Compositionally Modulated TFT Active Region for Low Leakage

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing thin film transistors (TFTs) made of oxide semiconductors face challenges in integration with previously fabricated devices due to high processing temperatures, which can damage front-end-of-line (FEOL) and middle end-of-line (MEOL) devices.

Innovation Solution

The formation of thin film transistors with a compositionally-modulated active region, including a continuous bottom gate dielectric layer and active layer, minimizes surface leakage and allows for direct contact between source and drain electrodes, using semiconducting metal oxides like indium gallium zinc oxide (IGZO) and a vertical compositional modulation to reduce leakage current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high processing temperatures are used to fabricate oxide semiconductor TFTs, then device performance is improved, but previously fabricated FEOL and MEOL devices are damaged

Engineering Contradiction:

Improvedevice performanceVSAvoiddamage to previously fabricated devices

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the temperature parameter of the fabrication process from high temperature to low temperature (below 450°C, preferably below 400°C). This parameter change allows the TFT to be fabricated without damaging previously fabricated FEOL and MEOL devices, while still achieving acceptable device performance through optimized low-temperature processing techniques

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a compositionally-modulated active region with different material compositions at different locations within the active layer. This local quality variation creates regions with different properties (e.g., higher mobility regions, lower resistance regions) that optimize device performance without requiring high processing temperatures

Inventive Principle:

Principle #3Local quality

2Reliability

If a compositionally-modulated active region is used, then surface leakage is reduced, but manufacturing complexity increases

Engineering Contradiction:

Improvesurface leakage reductionVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The active region is segmented into multiple layers or zones with different compositions (e.g., first active layer, second active layer with different stoichiometry). This segmentation allows each layer to perform specific functions (e.g., one layer for high mobility, another for low leakage), reducing overall surface leakage while maintaining manageable manufacturing complexity through sequential deposition processes

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS12402358B2Thin film transistor including a compositionally-modulated active region and methods for forming the same

Publication Date: 2025.08.26 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A thin film transistor includes an active layer and at least one gate stack. The active layer may be formed using multiple iterations of a unit layer stack deposition process, which includes an acceptor-type oxide deposition process and a post-transition metal oxide deposition process. A surface of each gate dielectric within the at least one gate stack contacts a surface of a respective layer of the oxide of the acceptor-type element so that leakage current of the active layer may be minimized. A source electrode and a drain electrode may contact an oxide layer providing lower contact resistance such as a layer of the post-transition metal oxide or a zinc oxide layer within the active layer.