NASA’s Glenn Research Center has developed nanoionic-based radio frequency (RF) switches for use in devices that rely on low-power RF transmissions, such as automotive systems, RFID technology, and smartphones. These groundbreaking nanoionic switches operate at speeds of semiconductor switches, and are more reliable than microelectromechanical systems (MEMS) switches while retaining the superior RF performance and low power consumption found in MEMS, all without the need for higher electrical voltages. In this new process, metals are photo-dissolved into a chalcogenide glass and packaged with electrodes and a substrate to form a switch. Since the nanoionic-based switch is electrochemical in nature, it has certain advantages over switches that are mechanically based, including nonvolatility, lack of moving parts that can fail, ease and efficiency of activation, and ease of fabrication. This innovative device has the potential to replace MEMS and semiconductors in a wide range of switching systems, including rectifying antennas (rectennas) and other RF antenna arrays.
The nanoionic-based switches exploit the properties of some amorphous materials that can incorporate relatively large amounts of metal and behave as solid electrolytes. As with liquid electrolytes found in lead-acid batteries, for example, solid electrolytes consist of mobile ions that undergo oxidation/reduction reactions at the anode and cathode of the system. The ionic conductivity of such a material can be of the same order of magnitude as the electronic conductivity of a semiconductor, but without the drawbacks of an electromechanical device.
In the nanoionic switch, ions are formed at an anode and migrate into the solid electrolyte, while electrons are injected from a cathode and cause the growth of metal nanowires through the electrolyte from the cathode to the corresponding anode when a positive DC bias is applied. Once a nanowire has grown sufficiently to form an electrically conductive path between the electrodes, the switch is closed and no electric power is needed to maintain the connection, unlike in a MEMS or semiconductor-based switch. Moreover, the process of making the connection can easily be reversed by applying a negative bias, causing the wires to ungrow and the switch to open. Thus, NASA’s state-of-the-art device is a reversible electrochemical switch that can have geometric features as small as nanometers. The process time for making or breaking the connection is very brief — about a nanosecond. In addition, this nanoionic material can be deposited in such a way to form multilayer control circuits, which has the potential to minimize circuit footprints, reduce overall circuit losses, and provide unprecedented ease of integration.
The switch is powered by 1 volt, as opposed to 50 to 60 volts for MEMS, and uses conventional integrated-circuit fabrication techniques with as few as five processing steps. Potential applications include conformal antennas for automotive collision-avoidance systems and navigation, such as GPS; phased arrays for communications and data storage, especially in broadcasting and radar; rectennas in smart keys, safety devices, and other radio-frequency identification (RFID)-based devices; and sensing and diagnostic systems for healthcare, oil and gas, and utilities.