Stepwise High-Voltage Transfer for OTP Memory Gate Oxide Protection
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Solution Overview
Problem
One-time programmable (OTP) memory cells face issues with abnormal gate oxide breakdown when program voltage is instantaneously transferred, leading to excessive bulk current and potential read failures, which compromises the reliability of the memory cell.
Innovation Solution
A high voltage transfer device comprising a first PMOS transistor and a second PMOS transistor connected in series, along with an enable circuit and a level shifter, is used to gradually stepwise transfer the external high voltage to the program transistor, preventing instantaneous voltage transfer and reducing the risk of abnormal gate oxide breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If external high voltage is instantaneously transferred to the program transistor gate, then programming speed is improved, but abnormal gate oxide breakdown occurs leading to reliability degradation
Solution Approach 1:
The voltage transfer process is segmented into multiple stages using a two-stage voltage transfer architecture. The first voltage transfer unit transfers voltage from external high voltage terminal to intermediate voltage terminal, and the second voltage transfer unit transfers voltage from intermediate voltage terminal to program transistor gate. This segmentation allows gradual voltage application rather than instantaneous transfer, preventing gate oxide breakdown while maintaining programming speed.
Solution Approach 2:
The first voltage transfer unit performs preliminary voltage transfer to the intermediate voltage terminal before the second voltage transfer unit applies voltage to the program transistor gate. This preliminary action ensures that voltage is gradually built up through controlled stages, preventing sudden voltage spikes that could cause gate oxide breakdown while still achieving the required programming voltage level.
2Productivity
If program voltage is transferred quickly to improve productivity, then excessive bulk current flows causing read failures
Solution Approach 1:
The voltage transfer is divided into two sequential stages through separate voltage transfer units. The first unit charges the intermediate voltage terminal, and the second unit charges the program transistor gate from the intermediate terminal. This segmentation controls the rate of voltage application, preventing excessive bulk current while maintaining programming efficiency.
Solution Approach 2:
The intermediate voltage terminal acts as a mediator between the external high voltage terminal and the program transistor gate. By introducing this intermediate stage, the system can transfer voltage in a controlled manner, preventing direct instantaneous voltage application that would cause excessive bulk current while still achieving the required programming speed.
Data Source
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AI summary
An electronic device comprises a one time programmable (OTP) memory cell that includes a program transistor and a read transistor; and a high voltage transfer device configured to level-shift an external high voltage to an internal voltage, wherein the high voltage transfer device includes a first PMOS transistor having a first end connected to an external high voltage terminal, a second PMOS transistor having a first end connected to a second end of the first PMOS transistor and a second end connected to a gate of the program transistor, an enable circuit configured to receive an enable signal and generate a gate voltage of the second PMOS transistor, and a level shifter connected to the enable circuit by a feedback path and configured to generate a gate voltage of the first PMOS transistor based upon the gate voltage of the second PMOS transistor provided through the feedback path.