Self-Protected Level Shifter With High-Bias Gate Drive
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Solution Overview
Problem
The semiconductor industry faces challenges in driving the gates of transistors suitable for controlling higher voltages, particularly due to reductions in minimum feature size, which affects the reliability of level shifting circuits.
Innovation Solution
A level shifting system incorporating a self-protection bias generator circuit that generates an amplified signal to drive protection transistors, enabling the use of thick-oxide transistors to protect thin-oxide pull-down transistors and maintain desirable output voltage ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thick-oxide transistors are used to control higher voltages, then voltage control capability is improved, but device area increases due to larger feature sizes required for thick-oxide transistors
Solution Approach 1:
The transistor gate oxide is segmented into two distinct layers: a first oxide layer with first thickness for high voltage control, and a second oxide layer with second thickness for low voltage control. This segmentation allows each layer to be optimized for its specific voltage range, enabling thick-oxide transistors to control higher voltages without requiring proportionally larger device area, as the dual-layer structure provides enhanced voltage control efficiency.
2Productivity
If minimum feature size is reduced to increase integration density, then integration density is improved, but reliability of level shifting circuits deteriorates
Solution Approach 1:
Different regions of the transistor gate oxide are assigned different qualities through the dual-layer structure. The first oxide layer provides high voltage control capability with appropriate thickness for reliability, while the second oxide layer provides low voltage control with different thickness characteristics. This local quality differentiation allows the transistor to maintain reliable operation across both voltage domains even with reduced minimum feature sizes, thereby preserving level shifting circuit reliability while enabling higher integration density.
3Reliability
If additional process-specific components are added to protect thin-oxide transistors, then device protection is improved, but device complexity increases
Solution Approach 1:
The protection function for thin-oxide transistors is merged with the gate oxide structure itself by forming a dual-layer gate oxide. The first oxide layer with greater thickness inherently protects the transistor from high voltage damage, while the second oxide layer maintains low voltage operation. This merging of protection functionality into the existing gate structure eliminates the need for separate protection circuits or additional process-specific components, thereby providing device protection without increasing circuit complexity.
Data Source
AI summary
A semiconductor device and a method of operating the semiconductor device are disclosed. In one aspect, the semiconductor device includes a level shifting circuit configured to generate an output voltage in a second voltage domain corresponding to an input signal in a first voltage domain. The level shifting circuit includes a thick-oxide transistor and a thin-oxide transistor. The semiconductor device includes a bias generating circuit operatively coupled to the level shifting circuit and configured to generate a bias voltage substantially higher than a voltage of the input signal, and provide the bias voltage to a gate of the thick-oxide transistor, causing the level shifting circuit to generate the output voltage.