Novel Topologies for Highly-Scalable Non-Volatile NEMS Relays

Complementary metal oxide semiconductors (CMOS) are nearing the limits for supply voltage and energy efficiency, motivating the search for alternative technologies. Emerging technologies like resistive memory (ReRAM), magnetoresistive memory (MRAM), phase change memory (PCRAM), and ferroelectric memory (FeRAM) offer scalable alternatives to CMOS, but are limited in either reliability, threshold voltage, or power consumption. Microelectromechanical system (MEMS) relays have gained interest as an energy efficient alternative to solid-state technologies due to the low leakage, abrupt switching, and high on/off ratios associated with mechanical contacts. A wide range of actuation methods are used in MEMS relays including electrostatic attraction, piezoelectric expansion, and thermal expansion. Common to these actuation methods is the use of a flexure to provide constraint or restoring force to overcome contact adhesion. These flexures prevent MEMS relays from scaling to dimensions comparable to CMOS devices.
This dissertation focuses on the development of the Phase Change NEMS Relay (PCNR), a novel non-volatile mechanical relay that eliminates the use of flexures and addresses the limited scalability of traditional MEMS relays. Phase change materials like GeTe can support crystalline and amorphous states at room temperature, which differ in material properties. Converting GeTe from the crystalline to amorphous state requires melting and quenching the GeTe. The PCNR is the first device to exploit the large 10 % volume change between the crystalline and amorphous states of GeTe in an actuator for mechanical displacement.
The PCNR is fabricated and tested with heater dimensions as small as 1 μm wide by 3 μm long and an air-gap of 20 nm. Actuator expansion is measured to be 26 nm, and switching is demonstrated with on and off times of 300 ns and 600 ns, respectively. On state resistance is measured to be 260 Ω and non-volatility is demonstrated for over 24 hours. Off state leakage is measured as low as 10-14 A. Scaling analysis shows a path towards CMOS comparable device sizes (5 nm wide by 20 nm long heater) as well as lower than CMOS actuation voltage (0.52 V). Actuation energy is predicted to be as low as 1.8 pJ with a 1.8 ns actuation time.