Nanoscale electromechanical (NEM) switches can be used as relays, transistors, logic devices, and sensors, and compared with conventional semiconductor switches offer reduced power consumption and improved ON/OFF ratios. NEM switches operate by controlling the contact between terminals, where a physical gap is typically overcome by applying large voltages (4–20 V) across the terminals. This prevents low-power applications and strong adhesion forces can occur that dominate over the restoring force. Overcoming these problems, a group of researchers at the Korea Advanced Institute of Science and Technology (KAIST) and the Korea National NanoFab Center (NNFC) recently fabricated NEM devices with ultrathin physical gaps by creating a curved or “pipe clip” suspended electrode structure. These operate below 1 V and exhibit negligible leakage current and on/off ratios of 1 × 106.
As described in a letter published online on November 25, 2012 in Nature Nanotechnology (DOI: 10.1038/NNANO.2012.208), Jeong Oen Lee of KAIST and co-researchers used a high-density plasma (HDP) method to deposit a sacrificial SiO2layer that was sandwiched between tungsten//tungsten/titanium electrodes. This resulted in an ultrathin gap of <10 nm between the electrodes.
Electric-field distribution of the traditional plane structure (upper) and the proposed pipe clip structure (lower) for a nanoscale electromechanical switching device. Reproduced with permission from Nature Nanotech. 8 (2013), DOI: 10.1038/nnano.2012.208; p. 36. © 2013 Macmillan Publishers Ltd.
The researchers used three-dimensional finite-element simulations to evaluate the electromechanical characteristics of the pipe clip structure, and to compare them with a plane structure. As shown in the figure, large forces exist near the small gap regions due to the quadratic nature of the electrostatic force. Electrical characterization showed repeatable switching near 400 mV with a very small subthreshold slope of 10 mV/dec.
This unique device structure addresses key requirements of low-voltage operated NEMs through a small physical gap (~4 nm), minimized physical contact to reduce adhesion forces, and straightforward fabrication using the sacrificial trenched-layer method.
