Evolution in cryogenic electronics can improve quantum computing and more
Cryogenic electronics are essential for various scientific and technological applications, especially in the quantum computing area. As quantum computers scale up in size and complexity, managing these cryogenic conditions becomes challenging. Each qubit requires its own set of control and readout lines, which can generate heat and cause interference. This causes qubits to fall out of their quantum state and compromise the accuracy of quantum operations. To counter this, part of the control and readout electronics needs to be placed inside a cryostat, a container that maintains extremely low temperatures. This placement reduces the need for heat-conducting cables but is constrained by the limited cooling power of the cryostat, meaning it can only remove a certain amount of heat. Power-efficient implementations are therefore required. The EU-funded research project SEQUENCE has developed dedicated cryogenic transistors and transistor models that significantly reduce the design margins for cryogenic circuit operation.
A new generation of cryogenic electronics
SEQUENCE made significant progress in understanding and modelling transistor behaviour in cryogenic conditions. Advanced transistor models, which accurately describe the physics of transistor operation in cryogenic conditions, have been crucial in reducing power consumption in key circuits. These included low-noise amplifiers and their arrays implemented in III-V high-electron-mobility transistor technology,” explains Lars-Erik Wernersson, SEQUENCE project coordinator. Furthermore, this knowledge helped the team to characterise the transistors in detail using 28-nm FDSOI (fully depleted silicon-on-insulator) technology. These transistors were utilised in high-performing 18-bit digital-to-analogue converters. The team has also designed new nanoelectronic devices to improve signal transmission and direction in high-frequency devices operating at extremely low temperatures. In particular, they utilised nanowires made from III-V semiconductors for routing radiofrequency signals at cryogenic temperatures. Their implementation reduced the number of ohmic contacts needed, which translates into lower signal loss.
3D integration bringing closer electronics to qubits
The consortium included 3D integration in the project, anticipating it would be an attractive route for scaling quantum systems. “The main benefits of this technology were the close proximity achieved between the quantum state and the control and readout electronics, and the simplified signal routing,” states Wernersson. This close proximity allows these electronics to directly interact with the qubits, controlling their states and reading out their responses. The team developed its first generation of circuits using vertical III-V nanowire technology. This allowed for an efficient integration of III-V transistors on silicon substrates, saving scarce material and enabling the use of larger wafers, namely, thin slices of semiconductor. Within the nanowires, a special type of heterostructure facilitated subthermal transistor operation below the threshold voltage, thus contributing to the power efficiency of the circuit. Exploring different options of the 3D integration, the team has also developed a demonstration of a 64-output programmable dynamic voltage biasing circuit, an achievement that offers flexibility in the circuit control, as well as a high level of complexity and programmability.
Beyond quantum computing
“The technology developed within SEQUENCE will not only benefit the development of quantum technologies. Semiconductor manufacturing companies have shown interest, as the project deepened understanding of transistor operation and refined transistor models describing cryogenic behaviour,” says Wernersson. According to him, the demonstrated circuit technology can also be applied in space technology, where temperatures range between 40 and 70 K. SEQUENCE explored circuit operation models that blend elements from both extremes – room temperature and cryogenic temperatures – thereby broadening the potential applications of the technology. There were also various attributes found in cryogenic electronics for quantum computing that can be useful for communication and radar technologies.
Keywords
SEQUENCE, cryogenic electronics, transistor, semiconductor, quantum computing, communication systems
