A microscale electromechanical logic
gate has been developed that can be reconfigured for seven different logic
functions using a simple frequency-driven configuration scheme^{1}. KAUST
researchers noted their new design could underpin a future computer architecture.

The microcomputer processors found in nearly all modern electronics are designed to process binary data—1s and 0s—through a series of logic gates to compute a solution. At their simplest, these logic gates take two inputs and produce a "true" or "false" output based on the type of gate, such as AND (both inputs are 1) or OR (either input is 1). With upwards of two billion logic gates, the latest computer processors have the capacity to process large arrays of bits simultaneously through enormous libraries of long and complex logic circuits. However, as only one logic circuit is activated for each arriving set of input bits, vast areas of modern chips can lie idle at any time.

KAUST researchers Abdullah Hafiz, Laxman Kosuru and Mohammad Younis have now developed an alternative type of logic gate that can be switched to a different mode of logic operation in between computations, presenting the possibility of configuring entire logic circuits for specific, efficient instructions for each operation.

“Our system is based on a microbeam that can be fabricated using conventional semiconductor fabrication processes, but which can be tuned to operate in any of the fundamental logic modes simply by changing the frequency of the driving voltage,” explained Younis. “The electrical current flowing through the microbeam generates heat. This causes the microbeam to expand, increasing its curvature and stiffness and changing its resonance properties. We then use the tuned resonance of the microbeam to build the logic gate.”

Although such electromechanical resonance schemes have been investigated before, this is the first time that such a logic gate has been constructed in a way that allows it to be changed dynamically at run time with such a versatile driving mechanism. This also allows it to be cascaded to form complete logic circuits. It is also the first electromechanical gate to be reprogrammable for all of the fundamental two-bit logic functions: AND, OR, NOT, NOR, NAND, XOR and XNOR.

“This is a major step towards achieving electromechanical computing devices,” said Younis. “It is well known that computational efficiency is reaching its physical limits. Unlike conventional transistors, which have flaws such as leakage at nanometer scale, electromechanical systems are predicted to be scalable even to the molecular level.”