3D Stackable Cryogenic InGaAs HEMT-Based DC and RF Multiplexer/Demultiplexer for Large-Scale Quantum Computing

Future large-scale quantum computing systems such as millions of qubits are expected to require highly scalable architecture. One of the possible and promising solutions is the three-dimensional (3D) co-integration of qubits and control/readout electronics on the same cryogenic chip. In this work, we demonstrate 3D stackable cryogenic InGaAs high-electron-mobility transistors (HEMTs) with extremely low power consumption. Futhermore, to control and readout millions of qubits with a limited cooling budget, we report the basic concept of the 3D integrated cryogenic DC and RF multiplexer/demultiplexer based on InGaAs HEMT for the first time. The 3D integrated InGaAs HEMTs with a gate length of $110 \mathrm{~nm}$ show a unity current gain cutoff frequency ($f \mathrm{~T})$ of 514GHz and unity power of 497GHz is the record-high value with the smallest power consumption ever reported in cryogenic RF transistors. The 3D stackable multiplexer/demultiplexer exhibit excellent routing capabilities both on DC and RF signal at $5 \mathrm{~K}$. Such 3D integrated multiplexer/demultiplexer will be one of the breakthrough technologies to successfully implement future large-scale quantum computing systems.