High-voltage transistor scaling circuit techniques for high-density negative-gate channel-erasing NOR flash memories

In order to scale high-voltage transistors for high-density negative-gate channel-erasing NOR flash memories, two circuit techniques were developed. A proposed level shifter with low operating voltage is composed of three parts, a latch holding the negative erasing voltage, two coupling capacitors connected with the latched nodes in the latch, and high-voltage drivers inverting the latch, resulting in reduction of the maximum internal voltage by 0.5 V. A proposed high-voltage generator adds a path-gate logic to a conventional high-voltage generator to realize both low noise and low ripple voltage, resulting in a reduction of the maximum internal voltage by 0.5 V. As a result, these circuit techniques along with high coupling-ratio cell technology can scale down the high-voltage transistors by 15% and can realize higher density negative-gate channel-erase NOR flash memories in comparison with the source-erase NOR flash memories.