A 0.02mm2 embedded temperature sensor with ±2°C inaccuracy for self-refresh control in 25nm mobile DRAM

This paper describes an all-CMOS embedded temperature sensor that directly controls the self-refresh period of a 25nm mobile DRAM. It occupies 0.02mm2, and achieves 0.04°C resolution and ±2°C accuracy from 20°C to 95°C after a single temperature trim. This performance is enabled by the use of dynamic threshold MOSFETs as temperature sensing devices, and by using chopping and trimming to mitigate the effects of device mismatch and process spread. The sensor consumes 9uW at a conversion rate of 7-kHz and a resolution of 50mK, which corresponds to a resolution FoM of 3.2pJK2. When used to control the self-refresh period of an 8GB mobile DRAM, the sensor reduces its standby current by 7x over a 20°C to 95°C range.