Taiwanese foundry TSMC has started building chips for a US start-up that plans to use stacked cells as a way of boosting the density of its write-once memory. Matrix Semiconductor wants to take the memories to a point where they can be as disposable as camera film or audio tape.
Matrix has designed a 3D chip structure that stacks write-once cells on top of each other. TSMC says it can build the devices using conventional process technologies.
By building up the memory array in three dimensions, Matrix says it can potentially reduce unit costs 10-fold, allowing for the shift to disposible chips. For the memory cell, the company has used an array of diodes. When programmed, small antifuses in the diodes are blown, forming a path that conducts in both directions.
In the circuit, the diodes are reverse biased when data is read so that large currents only flow through the antifuses that have been blown.
The diode array was proposed by Philips Semiconductor at the International Electron Device Meeting in 1996 as an alternative to one-time-programmable EPROM but with a density closer to that of mask rom.