Overview: Hybrid Piezoelectric MEMS/NEMS for Advanced Sensing and Wireless Communications
Sensors are nowadays found in a wide variety of applications, such as smart mobile devices, automotive, healthcare and environmental monitoring. The recent advancements in terms of sensor miniaturization, low power consumption and low cost allow envisioning a new era for sensing in which the data collected from multiple individual smart sensor systems are combined to get information about the environment that is more accurate and reliable than the individual sensor data. By leveraging such sensor fusion it will be possible to acquire complete and accurate information about the context in which human beings live, which has huge potential for the development of the Internet of Things (IoT) in which physical and virtual objects are linked through the exploitation of sensing and communication capabilities with the intent of making life simpler and more efficient for human beings.
This trend towards sensor fusion has dramatically increased the demand of new technology platforms, capable of delivering multiple sensing and wireless communication functionalities in a small foot print. In this context, Micro- and Nanoelectromechanical systems (MEMS/NEMS) technologies can have a tremendous impact since they can be used for the implementation of high performance sensors and wireless communication devices with reduced form factor and Integrated Circuit (IC) integration capability. In our recent work we have developed a new class of Aluminum Nitride (AlN) piezoelectric nano-plate NEMS resonant devices that can address some of the most important challenges in the areas of physical, chemical and biological detection and can be simultaneously used to synthesize high-Q reconfigurable and adaptive radio frequency (RF) resonant devices. By taking advantage of the extraordinary transduction properties of AlN combined with the unique physical, optical and electrical properties of advanced materials such as graphene, photonic metamaterials, phase change materials and magnetic materials, we have been able to implement multiple and advanced sensing and RF communication functionalities in a small footprint.
1. On-chip Reconfigurable Micro-Acoustic Radio Frequency Filters and Multiplexers for LTE Carrier Aggregation
In recent years the demand for highly reconfigurable radio frequency (RF) systems, capable of operating in the severely crowded and rapidly changing modern commercial and military spectral environment, at a reduced overall component count and with a reduced development cost compared to conventional multi-band radios, has been steadily growing. In this context, the implementation of high quality factor, Q, micro acoustic resonators with monolithically integrated switching and frequency reconfiguration functionalities will dramatically reduce loss associated with the filtering element enabling new radio architectures with enhanced spectrum coverage, whose implementation is currently prevented by the lack of such high performance and intrinsically reconfigurable components. Furthermore, the advent of LTE Carrier Aggregation (CA) as a means of increasing data rates in mobile device communication has triggered a paradigm shift in the design of acoustic filters. Whereas before CA the focus of filtering has been on supporting one telecommunication band at a time, now multiple bands will have to be supported simultaneously over the same antenna. Such carrier aggregation increases the requirements on filtering in LTE-Advanced (LTE-A) handsets. In particular, aggregation of two or more bands relatively close in frequency range can pose difficult problems. The only viable solution is to build multiplexers in which on-chip multi-frequency filters share a common antenna port and support the filtering needs of multiple bands.
We recently proposed and demonstrated, the monolithic integration of piezoelectric MEMS resonators and phase change material (PCM) RF switches as a solution towards the development of miniaturized, high performance, and highly reconfigurable RF components. Due to this unprecedented dense monolithic integration of high performance RF switches in the resonator design we were able to achieve the highest level of reconfigurability demonstrated to date. Our group demonstrated effective ON/OFF switching, impedance and frequency reconfiguration of AlN contour-mode resonators using ultra-miniaturized (2 μm x 2 μm) monolithically integrated phase change material switches with cut-off frequencies of ~ 5 THz. Such high reconfigurability was achieved without increasing the complexity of the device fabrication process (only 2 additional masks compared to a static resonator) or requiring substantial modification of the device layout (only an additional probing pad per via). We strongly believe that our proposed technology platform enables dense integration of resonators and switches with reduced resistive losses and capacitive loading effects setting a milestone towards the development of reconfigurable RF micro-systems capable of adapting to the rapidly changing RF environment and satisfying multiple wireless communications standards.
Furthermore, we recently proposed and demonstrated a new class of AlN MEMS resonators based on the piezoelectric transduction of a Lamé mode in the cross-section of an AlN plate. We identified them as Cross-Sectional-Lamé-Mode resonators (CLMRs). CLMRs rely on a coherent combination of the e31 and e33 piezoelectric coefficients of AlN to transduce a 2-dimensional (2D) mechanical mode of vibration, which is characterized by longitudinal vibrations along both the width and the thickness of the AlN plate. This feature enables the implementation of AlN CLMRs with high values of electromechanical coupling coefficient, kt2, exceeding 7%. In addition, due to dependence of such 2D mode on the lateral dimensions of the plate, CLMRs operating at significantly different frequencies can be lithographically defined on the same substrate without requiring additional fabrication steps. The possibility of attaining high kt2 and multiple operating frequencies on the same substrate, without additional fabrication steps, makes the CLMR-technology one of the best candidates for the implementation of multi-frequency filters on the same chip suitable for the aggregation of two or more bands (20 MHz bandwidth each) relatively close in frequency.
By integrating PCM switches with the CLMR-technology it will be possible to implement highly reconfigurable multiplexers in which a large number of filters are connected together through high performance RF PCM switches (with minimum capacitive loading effects) which can be dynamically programmed to aggregate specific bands, enabling scalable bandwidth (from 20 MHz up to 100 MHz) and the most agile and efficient use of the RF spectrum (needed to satisfy the needs of multiple markets exploiting aggregation of different bands).
1. G. Hummel, Y. Hui and M. Rinaldi, “Reconfigurable Piezoelectric MEMS Resonator using Phase Change Material Programmable Vias”, IEEE/ASME Journal of Microelectromechanical Systems (JMEMS), vol. 24, n. 6, pp. 2145-2151 (2015).
2. G. Hummel, Y. Hui and M. Rinaldi, “Highly Reconfigurable Aluminum Nitride MEMS Resonator Using 12 Monolithically Integrated Phase Change Material Switches”, Proceedings of the 18th International Conference on Solid-State Sensors, Actuators and Microsystems (Transducers 2015), Anchorage, Alaska, June 21-25, 2015, pp. 323-326.
3. G. Hummel and M. Rinaldi, “Switchable 2-Port Aluminum Nitride MEMS Resonator Using Monolithically Integrated 3.6 THz Cut-Off Frequency Phase-Change Switches”, Proceedings of the 2015 IEEE International Frequency Control Symposium (IFCS 2015), Denver, USA, April 12-16, 2015, pp. 706-708. [Winner of the Best Student Paper Award].
4. Y. Hui, Z. Qian and M. Rinaldi, “A 2.8 GHz Combined Mode of Vibration Aluminum Nitride MEMS Resonator with High Figure of Merit Exceeding 45”, Proceedings of the 2013 IEEE International Frequency Control Symposium (IFCS 2013), Prague, Czech Republic, July 21-25, 2013, pg. 930-932.
5. C. Cassella, Y. Hui, Z. Qian, G. Hummel and M. Rinaldi, “Aluminum Nitride Cross-Sectional Lamé Mode Resonators”, IEEE/ASME Journal of Microelectromechanical Systems (JMEMS), doi: 10.1109/JMEMS.2015.2512379 (2016).
6. C. Cassella, Z. Qian, G. Hummel, and M. Rinaldi, “1.02 GHz Aluminum Nitride Cross Sectional Lame’ Mode Resonator with High kt2 Exceeding 4.6%”, Proceedings of the 29th IEEE International Conference on Micro Electro Mechanical Systems (MEMS 2016), Shanghai, China, 24-28 January 2015, in press.
2. Plasmonic Piezoelectric Nanomechanical Resonators for Spectrally Selective Infrared/THz Sensing and Imaging
We recently proposed an innovative Infrared/THz sensor technology based on an ultrathin piezoelectric plasmonic metasurface forming the vibrating body of a nanomechanical resonator with unprecedented optical and electromechanical performance. By combining plasmonic and piezoelectric electromechanical resonances, we demonstrated efficient transduction of vibration in a nanomechanical structure with a strong and polarization independent absorption coefficient over an ultrathin thickness, addressing all fundamental challenges associated with the development of performing resonant IR detectors. Thanks to these unique attributes we recently demonstrated a fast, high resolution, uncooled infrared detector with ~80% absorption for an optimized spectral bandwidth around 8.8 μm. This work has set a milestone towards the development of a new technology platform based on the combination of nanoplasmonics and piezoelectric nano electro mechanical systems, which can potentially deliver fast (100s μs), high resolution (NEP as low as ~1pW/Hz1/2), and spectrally selective uncooled IR detectors suitable for the implementation of high-performance, miniaturized and power efficient IR/THz spectrometer and multi-spectral imaging systems. This is the topic of our NSF CAREER project which is exploring tremendous research and education opportunities at the intersection of NEMS and photonic metamaterial areas to attempt for the first time to develop a plasmonic piezoelectric nanomechanical resonator technology for uncooled and spectrally selective infrared/THz sensing and imaging. The unique integration and co-design of photonic metamaterials with a piezoelectric NEMS technology sought in this CAREER project will open up a vast and untouched field of research with plenty of room for career building explorations.
1. Y. Hui, Z. Qian and M. Rinaldi, “Resonant Infrared Detector Based on a Piezoelectric Fishnet Metasurface”, Proceedings of the 2015 IEEE International Frequency Control Symposium (IFCS 2015), Denver, USA, April 12-16, 2015, pp. 630-632.
2. Y. Hui and M. Rinaldi, “Spectrally selective infrared detector based on an ultra-thin piezoelectric resonant metamaterial”, Proceedings of the 28th IEEE International Conference on Micro Electro Mechanical Systems (MEMS 2015), Estoril, Portugal, 18-22 January 2015, pp. 984-987.
3. Y. Hui, Z. Qian, G. Hummel and M. Rinaldi, “Pico-Watts Range Uncooled Infrared Detector Based on a Freestanding Piezoelectric Resonant Microplate with Nanoscale Metal Anchors”, Proceedings of the 2014 Solid-State Sensors, Actuators and Microsystems Workshop (Hilton Head 2014), Hilton Head Island, 8-12 June, 2014, pp 387-390.
4. Z. Qian, R. Vyas, Y. Hui,and M. Rinaldi, “High Resolution Calorimetric Sensing Based on Aluminum Nitride MEMS Resonant Thermal Detectors”, Proceedings of the 2014 IEEE Sensors Conference, Valencia, Spain, 2-5 November, 2014. pp. 986 – 989.
5. Y. Hui and M. Rinaldi, “High Performance NEMS Resonant Infrared Detector Based on an Aluminum Nitride Nano Plate Resonator”, Proceedings of the 17th International Conference on Solid-State Sensors, Actuators and Microsystems (Transducers 2013), Barcelona, Spain, 16-20 June 2013, pg. 968-971.
6. Y. Hui and M. Rinaldi, “Fast and High Resolution Thermal Detector Based on an Aluminum Nitride Piezoelectric Microelectromechanical Resonator with an Integrated Suspended Heat Absorbing Element”, Applied Physics Letters, 102, 093501 (2013).
3. Two-dimensional-Materials-Enhanced Nanoelectromechanical Devices
Graphene, the thinnest known material in the universe with high electrical conductivity and ultra-low mass. Aluminum Nitride, a high quality and efficient piezoelectric material compatible with normal semiconductor process. By integrating these two materials and harnessing their unique characteristics, a radically new NEMS technology based on ultra-thin, low mass and high frequency Graphene-AlN nano plate resonators is born:
We recently demonstrated that a virtually mass-less and strain-less single-atom-thick graphene is perfectly capable of confining Radio Frequency (RF) fields within the active volume of a piezoelectric NEMS resonator, thereby allowing graphene-electrode based piezoelectric NEMS resonators to operate at their theoretical “unloaded” frequency-limits, with significantly improved electromechanical performance compared to metal-electrode counterparts, despite their reduced volumes. This represents a dramatic trend-inversion in the common knowledge regarding the scaling of piezoelectric electromechanical resonators. We strongly believe that by strategically coupling the unique electronic, optical and physical properties of 2D materials (beyond graphene) with the highly efficient piezoelectric transduction in AlN nano-plates, it will be possible to develop an innovative, intrinsically-tunable and switchable NEMS technology platform capable of delivering highly reconfigurable and adaptive radio frequency (RF) systems and photonic devices.
This technology was featured in a spotlight article on Nanowerk.com: “Graphene electrodes revolutionize the scaling of piezoelectric NEMS resonators”.
1. Z. Qian, F. Liu, Y. Hui, S. Kar and M. Rinaldi,“Graphene as a Massless Electrode for Ultrahigh-Frequency Piezoelectric Nanoelectromechanical Systems”, Nano Letters, 15 (7), pp. 4599–4604, 2015.
2. Z. Qian, Y. Hui, F. Liu, S. Kar and M. Rinaldi, “1.27 GHz Graphene-Aluminum Nitride Nano Plate Resonant Infrared Detector”, Proceedings of the 18th International Conference on Solid-State Sensors, Actuators and Microsystems (Transducers 2015), Anchorage, Alaska, June 21-25, 2015, pp. 1429-1432. [Winner of the Outstanding Paper Award]
3. Z. Qian, Y. Hui, F. Liu, S. Kar and M. Rinaldi, “Chemical Sensing Based on Graphene-Aluminum Nitride Nano Plate Resonators”, Proceedings of the IEEE Sensors 2015 conference, Busan, South Korea, November 1-4, 2015, pp. 1-4.
4. Z. Qian, Y. Hui, F. Liu, S. Kar and M. Rinaldi, “Single Transistor Oscillator Based on a Graphene-Aluminum Nitride Nano Plate Resonator”, Proceedings of the 2013 IEEE International Frequency Control Symposium (IFCS 2013), Prague, Czech Republic, July 21-25, 2013, pp. 559-561.
5. Z. Qian, Y. Hui, F. Liu, S. Kar and M. Rinaldi, “245 MHz Graphene-Aluminum Nitride Nano Plate Resonator”, Proceedings of the 17th International Conference on Solid-State Sensors, Actuators and Microsystems (Transducers 2013), Barcelona, Spain, June 16-20, 2013, pp. 2005-2008.
4. Ultra-Sensitive Integrated RF NEMS Magnetoelectric Sensors for Electro-Magneto-Brain Activity Map
Magnetoencephalography (MEG) is a widely used brain activity recording technique based on the measurement of magnetic fields generated by the brain. MEG has added a useful dimension to neurological research by providing a measure of brain activity which is not altered by the skull and other tissue surrounding the brain – as opposed to electroencephalography (EEG). State-of-the-art MEG, however, uses SQUID (superconducting quantum interference device) magnetometers, which operate at cryogenic conditions and require an expensive, fixed recording environment. Ultra-sensitive nanoscale magnetic sensors operating at room temperature could dramatically alter what is possible throughout the entire recording spectrum. Nanofabricated neural probes with arrays of nano-sized magnetic sensors, could provide a novel view of neural dynamics at the scale of individual neurons. This technological jump would dramatically reshape the landscape for understanding and treating brain function and dysfunction. Recently, we demonstrated a self-biased AlN/FeGaB magnetoelectric sensor based on a very high frequency (VHF) magnetoelectric NEMS nano-plate resonator. The efficient on-chip piezoelectric actuation and sensing of a high frequency bulk acoustic mode of vibration in a nano-plate structure, instead of a beam, has enabled the fabrication of a high frequency and high power handling resonator with power efficient transduction. At the same time the strong magnetostrictive coupling between the FeGaB magnetic film and the AlN piezoelectric nano-plate resonator has guaranteed ultra-high sensitivity of the device resonance frequency to DC magnetic field (due to the magnetic field induced variation of the device Young’s modulus, delta-E effect). Thanks to these unique features, we recently demonstrated a low limit of detection for DC magnetic fields of ~300 pT in unshielded environment. We strongly believe that this new class of compact, CMOS compatible and ultra-sensitive integrated RF NEMS magnetometers is ideally suited to sensing neural signals at room temperature. This is the topic of our Keck foundation project. Our goal is to trigger a major leap forward for both research and clinical use, by creating nanofabricated neural probes for room temperature electro-magnetoencephalography (EMEG). This research will lead to the most sensitive nanoscale room-temperature magnetometers, and new instruments that allow activating and recording the electric and magnetic signals of individual neurons. Portable and cost effective EMEG neural probes will lead to transformative advances in brain research, and in the diagnosis and treatment of brain disorders.
1. Y. Hui, T. Nan, N. Sun, M. Rinaldi, “High Resolution Magnetometer based on a High Frequency Magnetoelectric MEMS-CMOS Oscillator”, IEEE/ASME Journal of Microelectromechanical Systems (JMEMS), vol. 24, no. 1, pp. 134-143, 2014.
2. T. Nan, Y. Hui, M. Rinaldi, N. Sun “Self-Biased 215MHz Magnetoelectric NEMS Resonator for Ultra-Sensitive DC Magnetic Field Detection”, Scientific Reports, 3, Article number: 1985. (2013).
3. Y. Hui, T. X. Nan, N. X. Sun and M. Rinaldi, “Ultra-Sensitive Magnetic Field Sensor Based on a Low-Noise Magnetoelectric MEMS-CMOS Oscillator”, Proceedings of the 2014 IEEE International Frequency Control Symposium (IFCS 2014), Taipei, Taiwan, May 19-22, 2014, pp.1-3.
4. Y. Hui, T. X. Nan, N. X. Sun and M. Rinaldi, “MEMS Resonant Magnetic Field Sensor Based on an AlN/FeGaB Bilayer Nano-Plate Resonator”, Proceedings of the 26th IEEE International Conference on Micro Electro Mechanical Systems (MEMS 2013), Taipei, Taiwan, 20-24 January 2013, pp. 721-724.