Digital transistors—assembled by the billions in today's computer chips—act as near-perfect electronic switches. In the "on" position, achieved when an above-threshold voltage is applied to the device, the transistor allows current to flow. When the switch is off, the transistor prevents the flow of current. The on/off positions of the switch translate into the 1s and 0s of digital computation.
Although these 1s and 0s are fundamental to the operation of a computer, complex computations require that the data be stored in memory in order to be useful. In today's chips, memory relies on another device, in addition to the transistor: a capacitor that stores electric charge. The capacitor is empty when the transistor is switched off and flooded with electric charge when the transistor switches on. The charge on the capacitor then preserves the 1 or 0 of the transistor's switch state.
Researchers at the National Institute of Standards and Technology (NIST) and their colleagues at Brown University have now observed that at temperatures about three degrees above absolute zero (3K), a transistor can serve as its own memory storage device, obviating the need for a capacitor. By a process known as impact ionization, extra electric charges are generated inside the transistor. At low temperatures, some of these extra charges can be trapped in the transistor body, affecting the flow of current and providing a way to store memory of the "1" state.
The finding, reported online July 29 in Applied Physics Letters, could lead to the development of more compact control circuitry for low-temperature sensors and quantum information devices. For example, cold transistors could interface with and read out the data from proposed solid-state qubits—the quantum analog of the bits (1s and 0s) of a conventional computer, which require temperatures as low as 25 thousandths of a degree above absolute zero.
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