Flexible amorphous-silicon non-volatile memory

The development of a flexible, rewritable, non-volatile memory (NVM) that is implemented on a standard, low-temperature a-Si:H process without additional mask steps is reported. This NVM is a part of a flexible-display system. Each NVM cell is composed of differentially configured thin-film-transistors (TFTs). The cell reads out one of two stable states depending on the relative threshold voltages of the differentially configured TFTs. Information is stored in each cell by increasing the threshold voltage of one differential TFT or the other, utilizing the well-known electrical-stress degradation intrinsic to a-Si:H TFTs. The stored information is retained indefinitely with no applied power. A test array of individually addressable NVM cells has been successfully fabricated and tested on flexible stainless-steel substrates. Read and write operation, as well as preliminary reliability measurements, are described. The design is readily scalable to large memory arrays.