Series Pass Transistor Block Selection for High-Voltage Flash Erase
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Solution Overview
Problem
Related art block selection circuits in flash memory are vulnerable to high voltages during program and erase operations, necessitating larger flash memory designs to accommodate durable pass transistors.
Innovation Solution
A block selection circuit with a series connected pass transistor structure that distributes high voltage influence across two transistors, reducing the size of individual transistors and enhancing durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single pass transistor is used in the block selection circuit, then the circuit area is reduced, but the transistor becomes vulnerable to high voltages during program and erase operations
Solution Approach 1:
The patent divides the single pass transistor into two series-connected pass transistors (first pass transistor and second pass transistor). This segmentation distributes the high voltage stress across multiple transistors, improving reliability while maintaining a compact circuit structure. Each transistor handles a portion of the voltage stress, preventing any single transistor from being overwhelmed by high voltages during program and erase operations.
2Reliability
If pass transistors are made larger to withstand high voltages, then high voltage durability is improved, but the overall flash memory size increases
Solution Approach 1:
By segmenting the voltage stress across two series-connected transistors, each transistor can be smaller in size while collectively handling the high voltage requirements. This segmentation approach allows the flash memory to maintain high voltage durability without requiring individually large transistors, thus preventing an increase in overall flash memory size.
Solution Approach 2:
The patent combines two pass transistors in a series configuration to work together as a unified blocking structure. This merging of functional elements allows the system to achieve high voltage durability through collective action rather than requiring any single transistor to be oversized, optimizing the balance between reliability and compactness.
3Reliability
If two pass transistors are connected in series to distribute high voltage, then high voltage durability is improved, but the circuit complexity increases
Solution Approach 1:
The segmentation into two pass transistors with series connection provides a straightforward implementation that enhances reliability. The control logic remains relatively simple, with each transistor governed by its own driver circuit that responds to selection signals. This segmented approach improves high voltage durability without introducing excessive complexity in the block selection circuit architecture.
Data Source
AI summary
A flash memory includes a memory block connected to word lines, an address decoder that selects one or more of the word lines, a first pass transistor connected to the address decoder, a second pass transistor connected in series with the first pass transistor and connected to one word line among the word lines, a first driver circuit that controls a gate voltage of the first pass transistor based on a first enable signal, and a second driver circuit that controls a gate voltage of the second pass transistor based on a second enable signal. Based on the memory block being an unselected memory block during an erase operation, the first driver circuit controls the first pass transistor to be in a floating state, the second driver circuit controls a power voltage to be provided to a gate of the second pass transistor.