Integrated circuits are key components that control various electronic devices around us, such as PC, smartphones, automobiles, and home appliances. The basic building blocks of integrated circuits are transistors. Since the performance of transistors changes with temperature, the integrated circuits must be designed for its target operation temperature considering the temperature-dependent characteristics of transistors. Typical integrated circuits are designed to operate at room temperature (approximately 300 Kelvin), while some applications, such as automotive, in underground resource mining, and in space and aviation industries, require different operation temperatures. In recent years, integrated circuits for qubit control operating at cryogenic temperatures have been developed for realizing large-scale integrated quantum computers. This technology enables large-scale integration of qubits by controlling the qubits inside a refrigerator where the qubits are placed. When superconducting qubits or silicon qubits are used, the control circuits operate at 4 Kelvin (minus 269.15 degrees Celsius). However, the transistor characteristics at low-temperature such as 4 Kelvin (-269.15 degrees Celsius) deviate from the extension of conventional theory toward low-temperature. Although the recent progress revealed much about the transistor characteristics at low-temperature, the switching characteristics, one of the most fundamental parameters that determine the performance of transistors, remain a mystery and its physical model has not been established. Therefore, the elucidation of the switching characteristics of transistors operating at low-temperature is not only essential for a fundamental understanding of semiconductor physics, but is also an important unsolved problem for quantum computing applications.

Researchers at AIST have elucidated the low-temperature operation mechanism of transistors, which had been a mystery until now.

The performance of transistors, which are building blocks of integrated circuits, change depending on the temperature. Therefore, understanding the transistor characteristics at their operating temperatures is important for designing integrated circuits. Recently, integrated circuits for qubit control operating at temperature as low as 4 Kelvin (-269.15 °C) have been developed for realizing large-scale integrated quantum computers. However, the switching characteristics of transistors at low-temperature such as 4 Kelvin (-269.15 °C) cannot be explained by the conventional semiconductor physics and have remained a mystery. In this research, by measuring the transistor characteristics at deep cryogenic temperature of 0.015 Kelvin (-273.135 °C), which is two orders of magnitude lower than the operating temperature of 4 Kelvin (-269.15 °C), it was revealed that the electron capture at oxide/semiconductor interface trap determines the switching characteristics of transistors. This is a new finding that unravels a remaining mystery in low-temperature semiconductor physics and will contribute to improving the performance of quantum computers.