Internal Voltage Generating Circuit for Semiconductor Memory
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Solution Overview
Problem
Semiconductor memory devices experience threshold voltage increases at low temperatures, leading to insufficient charge transfer and sensing failures due to constant back bias voltage, which is not adequately adjusted for temperature changes.
Innovation Solution
An internal voltage generating circuit that compares temperature voltage with a variable reference voltage to control the back bias voltage, adjusting its level according to temperature changes through a temperature voltage generating unit, enable signal generating unit, and voltage pumping unit to maintain optimal voltage levels for efficient charge sharing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant back bias voltage is provided to control the threshold voltage, then the device operates stably at room temperature, but the threshold voltage increases too high at low temperature causing sensing failure
Solution Approach 1:
The back bias voltage is changed from a constant value to a dynamically adjustable value that varies with temperature. The voltage pumping unit adjusts the back bias voltage based on the comparison between temperature voltage and variable reference voltage, enabling the system to adapt to different temperature conditions while maintaining reliable operation.
Solution Approach 2:
The back bias voltage parameter is changed according to temperature conditions. At low temperatures, the back bias voltage is increased (pumped up) to compensate for the increased threshold voltage, while at room temperature, the constant back bias voltage maintains stable operation. This parameter adjustment resolves the contradiction between stability and temperature adaptability.
2Object-generated harmful factors
If the back bias voltage is increased to reduce leakage current, then leakage current decreases, but the threshold voltage becomes too high preventing sufficient charge transfer
Solution Approach 1:
The back bias voltage is dynamically adjusted based on temperature conditions rather than being constantly high. The enable signal generating unit activates the voltage pumping unit only when temperature voltage exceeds variable reference voltage, indicating low temperature conditions. This dynamic adjustment ensures sufficient charge transfer at low temperatures while maintaining low leakage current at high temperatures.
Solution Approach 2:
The back bias voltage parameter is changed according to temperature to balance leakage current reduction and charge transfer requirements. At low temperatures, the pumped-up back bias voltage compensates for threshold voltage increase, enabling sufficient charge transfer. At high temperatures, the normal back bias voltage level maintains low leakage current without excessive threshold voltage.
3Device complexity
If a constant back bias voltage is used, then the circuit design is simple, but sensing fails at low temperature due to insufficient charge sharing
Solution Approach 1:
The back bias voltage control circuit is made dynamic with temperature-dependent adjustment. The temperature voltage generating unit, enable signal generating unit, and voltage pumping unit work together to automatically adjust the back bias voltage based on temperature conditions, improving sensing accuracy at low temperatures while adding minimal circuit complexity.
Solution Approach 2:
The voltage pumping unit automatically adjusts the back bias voltage based on temperature conditions without external intervention. The temperature voltage and variable reference voltage comparison self-determines when pumping is needed, enabling the circuit to self-regulate and improve sensing reliability across temperature ranges with minimal additional control complexity.
Data Source
AI summary
A semiconductor memory device includes an internal voltage generating circuit and a memory cell. The internal voltage generating circuit is configured to compare a temperature voltage, which has a level varying with a predetermined slope according to a level change of an internal voltage, with a variable reference voltage, which has a level varying according to a temperature change, and pump the internal voltage. The memory cell includes a cell transistor having a threshold voltage controlled according to the internal voltage.