Nanomechanics

Theme II: Nanomechanics

The goal of the Nanomechanics team is to demonstrate low-voltage switching with nano-electromechanical (NEM) relays as ultra-low energy alternatives to the current-day transistor. In addition, guided by the Center’s System Integration team, strategies are investigated to apply zero-leakage NEM-based switching in a system application.

Typically, mechanical switches conduct current when two plates are in contact, and turn off current when the plates are separated. Since mechanical switches inherently have zero OFF-state current, they are promising solutions for the OFF-state leakage issue. Realizing that surface adhesion ultimately limits relay scaling, the Center has also focused on new approaches that go beyond voltage reduction through scaling and new device design. Instead, nanomechanics researchers at E3S pursue the concept of a tunneling relay whereby the electrical activation will occur when the two electrodes are brought into close proximity, but do not touch each other. The spacing of the electrodes can be controlled by spring-restoring forces or by folding molecular chains. The latter approach constitutes a molecular squeezable switch, or “squitch”. In addition, a NEM-based switch functioning by stretching molecular entities (a “stritch”) is pursued. Recently, successful operation of both the squitch and the stritch concepts has been demonstrated by E3S researchers.

Challenges

Current and future research within the Nanomechanics theme aims to resolve challenges in device design and scaling, reliability, and materials processing. To meet these challenges, researchers at E3S develop new fabrication processes to ensure sufficiently smooth surfaces inside the device. A major challenge is also to reduce the area of tunnel contact, while increasing the area of the electrostatic actuator. Furthermore, finding molecular building blocks with costume-designed structures and mechanical properties will be critical for optimized squitch and stritch operation.

Current Projects

Body-Biased Switch Design

Modeling studies by E3S Nanomechanics researchers identified a tunneling switch in which the spring-restoring force could counterbalance contact adhesion force. This body-biased approach is the basis for reducing the depth of the potential energy well created by contact adhesion and thereby overcoming the contact adhesion energy limit. Thus, it is possible for tunneling or non-contact switches to surpass the previously perceived switching energy limit of a direct contact nano-mechanical switch. The ultimate goal is the demonstration of reliable NEM switch (or relay) operation at or below 10 mV. The key challenge toward achieving this goal has remained the minimization, or even elimination, of the contact adhesion energy since contact stiction gives rise to hysteresis voltage., which would limit minimization of the switching energy.

Selected Recent Publications

• Reducing Adhesion Energy of Micro-Relay Electrodes by Ion Beam Synthesized Oxide Nanolayers, APL Materials, vol. 5, no. 3, pp. 036103, Mar 2017.
• Sub-50 mV NEM Relay Operation Enabled by Self-Assembled Molecular Coating, 2016 IEEE International Electron Devices Meeting (IEDM), San Francisco, CA, pp. 26.8.1-26.8.4., Dec 2016.
• Sub-100 mV Computing With Electro-Mechanical Relays, IEEE Trans. Electron Dev., vol. 64, no. 3, pp. 1323-1329, Mar 2017.

Squeezable and Stretchable Molecular Switches: “Squitch” and “Stritch” Designs

E3S researchers successfully demonstrated molecule-based tunneling nano-electro-mechanical switches (“squitches”) fabricated with metal-molecule-graphene tunneling junctions. Current work is focused on the development of new nanofabrication processes based on gold nanoplates and cubes, molecular monolayer deposition, and precision assembly. The goal of these new fabrication processes is to enable fabrication of squitches at the size scale and with the geometry required for low-voltage switching. In addition, a recent collaborative effort yielded a feasibility demonstration of piezoresistance in transition metal dichalcogenide (TMDC) monolayers strained using a micro-electro-mechanical actuator. This demonstration of a stretchable switch (“stritch”) opens the door to an intriguing avenue of low-voltage bandgap-modulated switching devices.

Selected Recent Publications

• Fabrication of Nanoscale Structures with Nanometer Resolution and Surface Uniformity, 30th IEEE MEMS International Conference, pp. 659-662, Jan 2017.
•  Redox Switchable Thianthrene-Cavitands, Synthesis, vol. 49, no. 2, pp. 358-364, Jan 2017.
• Tunneling Nanoelectromechanical Switches Based on Compressible Molecular Thin Films, ACS Nano, vol. 9, no. 8, pp. 7886-7894, Aug 2015.

NEM-Relay Based Circuits: Toward an Internet-of-Things Application

The ultra-low off-state leakage current in tunneling relays provides major advantages in the anticipated “Internet of Things”. A goal of Theme II is to demonstrate a working internet-of-things application, a data compression circuit to save radio communication energy by pre-compressing the sensor data. Ultimately, this will require a meaningfully-sized circuit, to digitally compress sensor data, consisting of over 1000 MEMs gates.

Selected Current Publications

• Embedded Nano-Electro-Mechanical Memory for Energy-Efficient Reconfigurable Logic, IEEE Electron Device Lett., vol. 37, no. 12, pp. 1563-1565, Dec 2016.
• Non-Volatile Nano-Electro-Mechanical Memory for Energy-Efficient Data Searching, IEEE Electron Device Lett., vol. 37, no. 1, pp. 31-34, Jan 2016.