Wide Band Gap Vertical TFT for 3D Memory Selection
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Solution Overview
Problem
Three-dimensional memory arrays using variable resistance memory elements face challenges in maintaining high breakdown voltage and low leakage current, which are crucial for efficient operation and minimizing unintended voltage application to unselected memory elements, especially during FORMING operations.
Innovation Solution
The use of a vertically oriented thin film transistor (TFT) selection device with a wide band gap semiconductor body, such as an oxide semiconductor, which provides high drive current, low leakage current, and high breakdown voltage, allowing for efficient selection and unselection of memory cells while reducing parasitic currents and simplifying the array architecture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional selection devices are used in 3D memory arrays, then device complexity is reduced, but breakdown voltage is insufficient and leakage current is high
Solution Approach 1:
The patent changes the material parameter of the selection device from conventional semiconductor to wide band gap semiconductor, which fundamentally alters the electrical characteristics to achieve high breakdown voltage and low leakage current while maintaining structural simplicity
Solution Approach 2:
The patent employs wide band gap semiconductor materials (such as silicon carbide or gallium nitride) combined with standard CMOS processes to create a composite device structure that leverages the superior electrical properties of wide band gap materials while maintaining manufacturing feasibility
2Reliability
If vertically oriented TFT selection devices with wide band gap semiconductor are used, then leakage current is reduced and breakdown voltage is increased, but manufacturing complexity increases
Solution Approach 1:
The patent transitions from planar TFT structure to vertically oriented TFT structure, utilizing the third dimension to achieve improved electrical performance through enhanced electric field control and reduced parasitic effects, while the fabrication follows adapted standard processes
Solution Approach 2:
The patent modifies the semiconductor material parameter to wide band gap materials, which inherently provide lower leakage current and higher breakdown voltage, offsetting the increased manufacturing complexity through material property enhancement
3Reliability
If higher voltage is applied during FORMING operations, then memory elements are properly initialized, but unintended voltage application to unselected elements increases
Solution Approach 1:
The patent introduces wide band gap semiconductor selection devices as intermediaries between the voltage source and memory elements, which act as voltage-controlled switches with high breakdown voltage capability to precisely control voltage application only to selected elements during FORMING operations
Solution Approach 2:
The patent changes the voltage threshold parameter of the selection device by using wide band gap semiconductor material, which has inherently higher breakdown voltage, enabling safe application of high FORMING voltages without affecting unselected memory elements
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 solution enables a more reliable and efficient 3D memory array with reduced leakage currents, lower power consumption, and simplified manufacturing, allowing for a larger number of addressed memory elements without errors in reading and within reasonable power supply capabilities.
Implementation Method 1
The use of a vertically oriented thin film transistor (TFT) selection device with a wide band gap semiconductor body, such as an oxide semiconductor, which provides high drive current, low leakage current, and high breakdown voltage
Data Source
AI summary
A 3D memory array having a vertically oriented thin film transistor (TFT) selection device that has a body formed from a wide energy band gap semiconductor is disclosed. The wide energy band gap semiconductor may be an oxide semiconductor, such as a metal oxide semiconductor. As examples, this could be an InGaZnO, InZnO, HfInZnO, or ZnInSnO body. The source and drains can also be formed from the wide energy band gap semiconductor, although these may be doped for better conduction. The vertically oriented TFT selection device serves as a vertical bit line selection device in the 3D memory array. A vertical TFT select device has a high drive current, a high breakdown voltage and low leakage current.