We demonstrate a cryogenic flash
memory on an undoped Si/SiGe heterostructure
by the modulation of its charge distributions. Two charge states are
created using a Si cap layer as a charge storage layer and manipulated
by electron tunneling between the Si cap and a buried Si quantum well
(QW). The device is programmed by increasing the gate bias to enhance
the tunneling rates of electrons in the buried Si QW to the Si cap.
The erasing step is performed by applying a negative gate bias to
deplete electrons trapped in the Si cap layer via tunneling to the
buried Si QW. The device has advantages over conventional flash memory
devices, since the programming and erasing operations are executed
via electron tunneling across the crystalline SiGe layer. We demonstrate
an endurance of 104 cycles and a retention time of 104 seconds with a memory window of threshold voltages of 1.4
V at 4 K, and the device is functional at temperatures up to 40 K.
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