Low Voltage I/O Structure with Thick Gate Overvoltage Protection
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Solution Overview
Problem
Existing input/output structures in integrated circuits face challenges in providing robust overvoltage/backdrive protection, especially at low temperatures and voltages, leading to poor alternating current performance and increased current consumption, due to the limitations of thick gate transistors and the inability to completely turn off native and depletion NMOS transistors.
Innovation Solution
Incorporating a thick gate native or depletion n-channel metal oxide semiconductor (NMOS) transistor as the transfer gate in the input/output structure, which prevents current from entering the structure at high output pad voltages and provides effective overvoltage/backdrive protection by maintaining a low threshold voltage, eliminating the need for p-channel transistors and reducing transistor size requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick gate transistors are used for overvoltage/backdrive protection, then protection capability is improved, but alternating current performance deteriorates and current consumption increases
Solution Approach 1:
The patent applies different gate thicknesses to different transistor locations: thick gate transistors are used specifically for overvoltage/backdrive protection at the output pad, while thin gate transistors are used for the main alternating current signal path. This local differentiation allows each region to optimize for its specific function, resolving the contradiction between protection capability and AC performance.
Solution Approach 2:
The patent segments the transistor population into two distinct groups based on gate thickness: thick gate transistors for protection functions and thin gate transistors for high-performance AC functions. This segmentation allows the system to simultaneously achieve robust protection and excellent AC performance without compromise.
2Ease of operation
If thick gate standard NMOS transistors are used, then they can be turned off at zero gate to source voltage, but native and depletion NMOS transistors cannot be completely turned off at low voltages
Solution Approach 1:
The patent changes the threshold voltage parameter of NMOS transistors by using native or depletion implants instead of standard implants. This parameter change allows the transistors to maintain a negative or near-zero threshold voltage, enabling them to be turned off at zero or near-zero gate to source voltages, which is critical for low-voltage operation.
3Reliability
If only thick gate transistors touch the output pad for ESD performance, then electrostatic discharge protection is improved, but transistor size requirements increase
Solution Approach 1:
The patent applies thick gate transistors locally at the output pad contact points for ESD protection, while using thin gate transistors for the internal AC signal path. This localized application of thick gate transistors provides adequate ESD protection without requiring all transistors to be large, thus reducing overall area consumption.
Data Source
AI summary
A system and method are disclosed for providing an integrated circuit low voltage thin gate input/output structure with thick gate overvoltage/backdrive protection. In an advantageous embodiment of the present invention, a transfer gate of the input/output structure comprises at least one thick gate native (or depletion) n-channel metal oxide semiconductor (NMOS) transistor that is connected to an output pad node of the input/output structure. The thick gate native (or depletion) NMOS transistor prevents current from the output pad node from entering the input/output structure when a voltage level of the output pad node is high.