No abstract
number of devices per area, but does not improve the power efficiency of an individual device. The advent of the internet of things has generated increased demand for ultralow power systems. A number of emerging technologies are being developed as ways to augment or replace CMOS for various computing applications. Some of these technologies include: resistive memory, [3,4] phase change memory, [5,6] magnetoresistive memory, [7,8] and ferroelectric field effect transistors. [9,10] A key feature common to these technologies is nonvolatility, [11] which is the ability of a device to hold its state without a power supply. These emerging memories suffer from their limited difference in resistance between the ON and OFF states (ON-OFF ratio). A low ON-OFF ratio poses a great challenge toward cascading long arrays of devices in memory intensive applications because the sensing margin is poor during the read operation. Furthermore, the nonzero OFF current leads to high leakage, resulting in greater static power consumption.MEMS-based mechanical relays, another emerging technology, have a large ON-OFF ratio due to the near zero leakage off state associated with an open mechanical contact. [12] MEMS relays have been demonstrated as nonvolatile devices as well, [13] but a major bottleneck to the adoption of mechanical relays is their scalability to cell sizes that are comparable to state-ofthe-art CMOS devices. Common MEMS relays use a flexure, [14] which limits scalability due to material limits and anchor sizes. We earlier reported a 11 µm × 1.5 µm nonvolatile mechanical actuator based on the volumetric expansion of GeTe phase change material. [15] This reversible volume expansion can be used to directly close an air-gap, eliminating the need for flexures and making for an inherently highly scalable device. A prototype nonvolatile device was then presented. [16] Here we report the detailed design and demonstration of a smaller device (3 µm × 1 µm) and a family of nonvolatile relays. These results demonstrate a path to scaling a MEMS relay with smaller area and lower voltage than a future foreseeable CMOS transistor. Device Operation and Results Operating PrincipleThe Phase Change NEMS relay (PCNR) is designed to address the limited scalability of existing MEMS relay designs while continuing to use mechanical contacts for a high ON-OFF ratio and while maintaining nonvolatile states. The PCNR takes The design, modeling, and experimental validation of a highly scalable phase change electromechanical relay are present. The Phase Change NEMS Relay (PCNR) is a nonvolatile mechanical relay actuated by the volumetric expansion of phase change material. GeTe is used as the active phase change material, and nonvolatile relay states are changed by converting it between amorphous and crystalline phases, which differ in volume by 10%. Phase conversion is induced by Joule heating an adjacent metal layer. Finite element analysis (FEA) models are developed to predict actuator temperature distributions and quench times for varied actuatio...
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