Enhanced read and write methods for negative differential resistance (NDR) based memory device
An enhanced method of writing and reading a memory device, such as an SRAM using negative differential resistance (NDR) elements), is disclosed. This is done through selective control of biasing of the active elements in a memory cell. For example in a write operation, a memory cell is placed in an intermediate state to increase write speed. In an NDR based embodiments, this is done by reducing a bias voltage to NDR FETs so as to weaken the NDR element (and thus disable an NDR effect) during the write operation. Conversely, during a read operation, the bias voltages are increased to enhance peak current (as well as an NDR effect), and thus provide additional current drive to a BIT line. Embodiments using such procedures achieve superior peak to valley current ratios (PVR), read/write speed, etc.
1. A method of operating a memory cell comprising a storage node coupled between a pull-up element and a pull-down element, the method comprising:
applying a first bias signal to at least one of the pull-up element and the pull-down element to attenuate an NDR operational characteristic of the at least one of the pull-up element and the pull-down element and set the storage node to an intermediate voltage;
writing a data value to the memory cell by adjusting the storage node from the intermediate voltage to one of an upper voltage and a lower voltage; and
applying a second bias signal to the at least one of the pull-up element and the pull-down element to enable the NDR operational characteristic of the at least one of the pull-up element and the pull-down element to latch the data value into the memory cell.
2. The method of claim 1 , wherein the intermediate voltage is approximately halfway between the upper voltage and the lower voltage.
3. The method of claim 1 , wherein applying the first bias voltage signal to the at least one of the pull-up element and the pull-down element comprises applying the first bias voltage signal to the pull-up element and the pull-down element.
4. The method of claim 3 , wherein applying the second bias voltage to the at least one of the pull-up element and the pull-down element comprises applying the second bias voltage signal to the pull-up element and the pull-down element.
5. The method of claim 1 , wherein the at least one of the pull-up element and the pull-down element comprises a first NDR FET.
6. The method of claim 1 , wherein the pull-up element comprises a first NDR FET and the pull-down element comprises a second NDR FET.
7. The method of claim 6 , wherein the first NDR FET and the second NDR FET are silicon-based NDR FET of the same type.
8. The method of claim 6 , wherein the first NDR FET and the second NDR FET are different types of silicon-based NDR FETs.