Micro-TEG Voltage Supplies for Spin Torque Oscillators

Abstract

Spin torque oscillators (STOs) can be viewed as current-controlled oscillators. Oscillations start if the current exceeds some critical value-threshold current. A low critical current is required to achieve a high output power. Recently, the critical current was reduced to as low as 0.1 mA and STO majority gate was proposed. To operate STO logic, an mV-level voltage source with output current greater than the critical current (0.1 mA), and very low impedance is needed. This paper proposes power supplies that use microthermoelectric generators (μTEGs) to convert heat into electric power. A complete analytical μTEG model was developed that includes all the relevant physical effects. This model is used to predict power and perform geometry optimization to maximize thermal energy conversion. We propose metallic thermocouples to realize the low impedance source and connect them electrically in parallel to deliver sufficient current. The proposed μTEG consists of four thermocouples connected in parallel both thermally and electrically. Thermo-legs are homogeneous and thermally isolated with a thermal isolation cavity to minimize heat leakage. Simulations with a 30-K temperature drop across μTEGs showed that the proposed structure can potentially integrate ~ 50 000 μTEGs/cm2 and efficiently harvest heat to supply new STO logic.