ZettaCore molecular memory is based on the properties of specially-designed molecules. We use these molecules to store information by adding or removing electrons and then detecting the charge state of the molecule. The molecules, called multi-porphyrin nanostructures, can be oxidized and reduced (electrons removed or replaced) in a way that is stable, reproducible, and reversible. In this way, molecules can be used as reliable memory locations for electronic devices. In many ways, each molecule acts like an individual capacitor device, similar to a conventional capacitor, but storing only a few electrons of charge that are accessible only at specific, quantized voltage levels. The key difference between ZettaCore memory and conventional memory is that as the size of a memory element becomes smaller, the properties of semiconductor or polymer materials change in undesirable ways, while the properties of our molecular capacitors remain the same. This allows scaling to very small size elements.
We design molecules to have the properties needed for a particular application. The most important property is the oxidation potentials – the energy required to remove one or more electrons. This energy is a quantum mechanical property of the whole molecule and is typically between 100 and 200 mV for each electron removed. For each molecule we design the value is exact and doesn’t vary. We have designed molecules with up to eight oxidation states, meaning we can remove up to eight electrons and detect the resulting state of the molecules using distinct, discrete voltages. Using multi-state molecular capacitors with quantized energy states, we can reliably store more than one bit of information in a single memory location.
Another property we design into our molecules is chemical self-assembly. This allows the molecules to attach only to a particular type of surface (for example, gold, silicon, various metals and oxides), to pack tightly on that surface, and to align properly on the surface for electronic operation. Because of chemical self-assembly, ZettaCore molecular memory chips can be manufactured using equipment and processes common in the semiconductor industry. Molecules are applied to an entire wafer by spraying or dipping and attach only to those exposed surfaces they are designed for. Unattached molecules are simply washed away from the other surfaces.
The diagram below shows the basic concepts of ZettaCore molecular memory. An individual molecule is shown in the lower left corner. This molecule has four states, so it stores two bits of information. Using chemical self-assembly techniques, the molecules are applied to all of the memory elements of an array. At each location in the array there may be between a few thousand and a million molecules (depending on the size of memory elements and the type of device structures being used). This provides excellent signal to noise characteristics and defect tolerance through redundancy. The failure of any single molecule will not affect the operation of a memory element.
The array is connected to custom-designed I/O circuits (not shown) fabricated using conventional logic that read and write the array.
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