The Antenna and Optical Systems Branch at NASA’s Glenn Research Center is working on many innovations in nanotechnology for use in communications applications. One such emerging field of nanotechnology receiving significant attention for its promising results is nanoionics. Nanoionics-based technologies employ ion transport and chemical change at the nanoscale, using oxidation/reduction reactions of ionic metal species in order to build conductive bridge contacts. These mechanisms can serve as the basis for many nanoscale devices and can help overcome some of the challenges inherent in microelectro-mechanical systems (MEMS)-based and solid-state-based devices for radio frequency (RF) applications.
NASA’s Nanoionics Advancement
Innovators at Glenn and their partners at Arizona State University have developed the initial design for the first-ever switching mechanism for microwave applications based on nanoionic materials. This novel innovation offers many advantages over RF MEMS-based systems that are often used for microwave applications:
- The switching process is non-volatile. Power is needed only to change ON/OFF states, not to maintain either state, resulting in fewer needed bias operations.
- Low energy requirements (only nJ are needed to operate the switch).
- The switch has no moving parts, lowering failure risk and increasing speed.
- Metal ion conductivity in this switch is comparable to electron conductivity in semiconductors, indicating that switching speeds can be competitive with solid-state switches.
- The fabrication process requires as few as five processing steps using common tools, significantly easing integration and reducing fabrications costs.
The Nanoionics-Based Switch operates via an electrochemical process in which mobile ions within a solid electrolyte form and remove metallic “bridges” to change the ON/OFF state. The present device features a simple planar geometry that supports novel device structures and simplified integration with microwave power distribution circuits. The geometry consists of two electrodes of dissimilar metals that are Au-plated onto a quartz substrate. A gap separates the electrodes, and a silver-saturated glass deposited within the gap represents the active area of the device. Operation is achieved by applying a positive voltage relative to the inert (non-oxidizable) electrode, inducing a silver-based conductive path and enabling the device to be turned ON. The device is turned to the OFF state by reversing polarity of the applied voltage, which removes the electrochemically created silver path.
In testing, the Nanoionics-Based Switch demonstrated:
- Insertion loss of better than ~0.5dB
- Isolation of >30dB
- Low voltage operation (1V)
- Low power (~μW) and low energy (~nJ) consumption
- Excellent linearity up to 6 GHz
Observed Limitations and Challenges
While the switch has low-voltage operation, higher voltages demonstrated faster oxidation-reduction rates of silver, and thus faster switching between states. Also, higher current limits reduced the resistive loss of the grown silver, but resulted in higher power required to operate the switch. Obviously, a trade-off between performance and power will play the most significant role in device design.
The switch demonstrates performance comparable to MEMS and solid-state-based RF switches in the aforementioned frequency range, but at much higher frequencies, its performance needs to be optimized. In addition, improving the repeatability of performance over several cycles is a challenge for the next phase of development.
What Applications Does NASA Envision?
Further development of the Nanoionics-Based Switch could lead to many novel device structures, notably the concept of a single-pole-N-throw switch (SPNT). Adding extra electrodes (ports) to the Nanoionics-Based Switch in contact with the active area would make an SPNT switch possible with minimal fabrication cost. Other applications would include multilayer control circuits for low-loss phased array antenna technology, minimizing phase shifter loss and reducing circuit complexity.
NASA Seeks Partners for Further Development
With further optimization, NASA’s Nanoionics-Based Switch offers potential advantages over state-of-the-art solid-state and MEMS-based microwave switches. NASA seeks partners interested in research and development toward improvement of device performance (repeatability, losses, frequency range), and extending use to the Ka band. These highly attainable improvements could result in a commercially viable product for potential partners.