Static RAMs with microwatt data retention capability

Static RAMs using undoped polysilicon load resistor cells can retain data at less than a nanowatt/bit. This allows large memories to be designed for low-power battery backup applications provided 1) all peripheral circuits can be powered down without disturbing the stored data, and 2) subthreshold leakages of `off´ transistors in the memory are at an adequately low level to maintain the stored data during battery backup. Novel circuitry has been developed which assures both conditions without compromising performance. These circuits have been used successfully in 4K and 16K static RAMs, with typical power dissipations of 5 and 12 μW, respectively. Data are retained in battery backup over a temperature range in excess of the specified 0-100°C, even with rapid skewing of the power supply voltage.