Gates that move by springing, and electromigration relays, could form the basis of 100MHz non-volatile logic with extremely low leakage.
So claims a heavy-weight research partnership formed between the University of Southampton, Japan's National Institute for Materials Science (NIMS), and the Hitachi Cambridge Laboratory.
"There will be huge benefits from the cooperation between the Southampton and NIMS teams," said Professor Hiroshi Mizuta of Southampton. "We will be cooperating closely in overcoming current technological bottlenecks."
Two devices have been invented: The electromechanical (EM) transistor at Southampton, and the atom transistor at NIMS.
Both have been demonstrated, and the partnership now has three years of funding to turn them into practical non-volatile logic.
Counter-intuitively, the electromechanical transistor has a classic mosfet structure with a gate insulator and no mechanical switching, whereas the atom transistor is not a mosfet, but a mechanical switch relying on fast electromigration.
Electromechanical transistor
"The electromechanical transistor has a suspended metal or polysilicon gate that is usually kept above the gate oxide with an air gap," Southampton's Mizuta told Electronics Weekly. "When you apply a gate bias, the gate descends onto the gate insulator and turns on the channel like a normal mosfet."
Once the bias is removed, the gate springs back and leaves the channel in its off-state - more off than if the gate had remained on the surface of the gate oxide, so leakage is lower, said Mizuta.
Inter-atomic forces mean the movement of the gate has some hysteresis - the gate engages at a different voltage than it disengages - and there are ways to set these two voltages either side of zero volts making the gate bistable - mechanically storing the transistors state even with no voltage applied to the circuit.
"To get non-volatility, we can add a silicon quantum dot to the gate which acts as charge storage and adds electrostatic force," explained Mizuta.
With channels around 100nm long, fast operation is expected from electromechanical transistors.
"Three dimensional numerical simulation and experiments show there are time two components: the mechanical motion is less than 10ns, and the time to charge the quantum dot is 1-2ns. The channel is much faster, so the total switching time will be a few nanoseconds," said Mizuta.
Atom transistor
Invented by Dr Tsuyoshi Hasegawa at NIMS and demonstrated in December last year, the atom transistor is a three terminal version of IBM's two-terminal e-fuse.
Potential on the gate (see diagram) causes copper atoms to separate and migrate through a layer of Ta2O5 high-k dielectric where they gather and short-out two terminals underneath.
A different gate potential pulls the copper atoms back to the gate, breaking the source-drain circuit.
Again, the device is bistable as the copper atoms stay where they are with no gate bias.
Operational polarity is such that the atom transistor can only act like an n-channel device, and the simplest form of the electromechanical transistor acts like a p-channel device, so both are required to make non-volatile logic with CMOS-like behaviour.
According to Mizuta, with more complexity it is possible to make electromechanical transistors with n-channel characteristics, opening-up the possibility of all-EM transistor non-volatile logic, and the invention of a p-channel equivalent atom transistor has not been ruled-out, so all-atom transistor non-volatile logic might also be possible.
Funded has come from the Engineering and Physical Research Council's (EPSRC's) strategic UK-Japan cooperative program with the Japan Science and Technology Agency.