100 NM Thick Aluminum Nitrade Based Piezoelectric Nano Switches Exhibiting 1 MV Threshold Voltage via Body-Biasing

This paper reports on the first demonstration of aluminum nitride (AlN) piezoelectric logic switches that were fabricated with ultra-thin (100nm) AlN films and exhibit a 1 mV threshold voltage via the body-biasing scheme. The application of a relatively low ( 10 cycles and, although the contact resistance was found to be high (~ 1 MΩ), the nano-films have functioned throughout to show high piezoelectric nano-film reliability. INTRODUCTION With the continuous scaling of the transistor the CMOS industry has recognized the emergence of some key problems that are proving to be serious obstacles to further miniaturization. Some of the major hurdles that need to be overcome involve the source-to-drain leakage in the standby state, the gate leakage because of ultra-thin dielectric layers, the inability to reduce operating power, the variation of threshold voltages over a wafer and the increasing effect of parasitics on the device performance. With miniaturization, transistors have become faster, but the gain in speed has come at a penalty in terms of standby power consumption. Also, with the CMOS transistors already switching in less than few nanoseconds, power is becoming a more relevant aspect to consider than speed. Keeping all these factors in mind the International Technology Roadmap for Semiconductors (ITRS) [1] has emphasized the need to develop alternate devices, like NEMS switches, that will consume less power in the standby state and will help in minimizing the transistor operating voltages. Mechanical switches have been a topic of research and investment for few decades. They have nearly zero standby leakage due to the presence of an air gap between the source and the drain terminals. In addition, they are characterized by a very sharp transition between their standby and on states. This transition is not governed, as in a semiconductor, by the modulation of carriers in the channel, but by the actual mating of contacts due to mechanical motion. Therefore, mechanical switches exhibit a subthreshold slope that is orders of magnitude lower than that of CMOS devices. Because of these characteristics they are the ideal candidate to lower power consumption in the standby state and operating voltages. Most of the mechanical switches developed to date have utilized electrostatic [2-3], magnetic [4], thermal [5] or piezoelectric [6-9] actuation mechanisms. These mechanical switches have not been commercialized on a large scale as they are not as reliable and as fast as the semiconductor transistors. Micromechanical switch reliability has been limited by the very stringent requirements on the on-resistance as dictated by radio frequency (RF) applications (i.e. few Ohm of contact resistance), which have so far been the most attractive for microswitches. When we consider the same devices for implementation of mechanical computing/logic, the main design challenge resides not in the loss due to the contact resistance but the speed of operation. According to these new guidelines a mechanical switch can operate with contact Figure 1: SEM of a nano-film based three-finger dual-beam AlN switch illustrating the source, drain, gate and body bias terminals. This nano-switch is being termed as a Mechanical Transistor. The figure above also shows its similarity with a Semiconductor Transistor shown on the right of the figure. Body Drain Gate Source