Ultra Miniature 1850 μm2 Ring Oscillator Based Temperature Sensor

Temperature sensing is a necessity in semiconductor products, in order to monitor die behavior and avoid thermal runaway, while achieving high performance. Integrated sensors are used to monitor and regulate numerous hot spots across the die to prevent reliability issues. As the hot spots are in the most congested areas of the chip, it is also desirable for the sensors to have a very small sensing element which can be placed close to the hot-spot. The sensors are also used to monitor the coldest parts of the chip to determine the required Vdd level. These functions require the sensors to be very compact as well as low energy. A ring oscillator based temperature sensor is presented in TSMCs 65nm node, with an area of 1850μm
²
. This sensor has a novel structure which is similar to a bandgap reference, with the BJT devices replaced by scaled ring oscillators. The sensor exhibits a 3-sigma inaccuracy of ±1°C near the throttle point, for hot-spot sensing, and ± 2.5°C over the -10°C to 110°C range. The power supply rejection is 2.4°C/V. The sensor consumes 0.94nJ per 10μs conversion and achieves a resolution FOM of 96pJ-K
²
.