Self-heating in cryogenic HEMTs for quantum computing readout applications

Quantum computers are becoming more and more relevant in today's world to compete with traditional computing solutions. To achieve such performance levels it is necessary to integrate the bulky control, bias, and readout electronics inside the dilution fridge to scale the number of qubits inside the quantum computer. Low noise amplifiers realized with InAlAs and InGaAs HEMTs are a viable option to transfer the readout amplification to the 4K stage. Self-heating of these devices in this operating condition is not fully characterized yet and this work wants to understand how this affects the area around the HEMT to evaluate future on-wafer integration. Novel sensing structures are proposed to build in-situ temperature monitoring with high versatility and integration possibilities. HEMTS and Schottky diodes temperature dependent electrical characteristics are used to assess the temperature of the substrate. This ensures high possibilities of integration, using the same processes to fabricate the device to be characterized and the ones used to sense. HEMT sensing devices show crosstalk problems and low sensitivity whereas the Schottky diodes provide linear and reliable results. Multiple arrays of devices are fabricated to gather a complete 2D heatmap around the device under test. Vertical temperature profiles show to be complementary with gate thermometry values performed on the same devices. Measurements at 300K prove that this approach represents a working methodology that may be integrated with other technologies. The sensing structure was used to obtain substrate heat dissipation at cryogenic temperature. Higher or compared self-heating has been reported in the literature on the device level but this work shows how this does not affect the area around the device. Measurements at 4K display values under the resolution of the sensing element at all locations characterized. This represents the possibility to position temperature sensitive devices (e.g. qubit) close to the amplifier, resulting in higher integration density.