Asymmetric Vertical TFT Selector for Low Off and High On Current
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Solution Overview
Problem
Existing vertical thin film transistors (TFTs) cannot sustain both an off current of less than 1 nanoamp and an on current of 100 microamps, making them inadequate for functioning as both pillar selectors and access line selectors in memory devices.
Innovation Solution
The development of an asymmetric vertical thin film transistor (TFT) design, where one end of the channel extends beyond one end of the gate, while the other end does not, allowing for improved current control and enabling the TFT to function effectively as both a pillar selector and an access line selector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional vertical TFT design is used, then the device structure is simple and symmetric, but it cannot sustain both low off current (<1 nanoamp) and high on current (100 microamps) simultaneously
Solution Approach 1:
The patent applies asymmetry by making one end of the channel extend beyond one end of the gate while the other end does not extend beyond the gate. This asymmetric configuration creates different electric field distributions at each end of the channel, enabling the TFT to achieve both low off current (<1 nanoamp) and high on current (100 microamps) simultaneously, resolving the technical contradiction between current control capability and structural simplicity.
2Adaptability or versatility
If a single TFT is designed to function as both pillar selector and access line selector, then device versatility is improved, but the current control requirements become more stringent and conflicting
Solution Approach 1:
The patent implements universality by designing a single asymmetric vertical TFT that can function as both a pillar selector and an access line selector. The asymmetric structure enables the device to meet the conflicting current control requirements of both selector roles: achieving low off current for pillar selection while maintaining high on current for access line selection, thus eliminating the need for separate specialized transistors.
Data Source
AI summary
Systems, methods, and apparatuses are provided for an asymmetric vertical thin film transistor selector. An apparatus includes first and second source/drain regions formed on a substrate, a channel separating the first source/drain region and the second source/drain region, and a gate separated from the channel by a gate dielectric material. The first source/drain region, the second source/drain region, the channel, and the gate form a vertical thin film transistor, a first end of the channel is coupled to the first source/drain region and extends beyond a first end of the gate, and a second end of the channel is coupled to the second source/drain region and does not extend beyond a second end of the gate that is opposite the first end of the gate. A contact in the substrate is coupled to the first source/drain region and a sense line is coupled to the second source/drain region.