About

Nicol McGruer is a Professor of Electrical and Computer Engineering at Northeastern University, with affiliated faculty status in Mechanical and Industrial Engineering. His research focuses on microfabrication, nanotechnology, and microsystems, including MEMS, NEMS, RF MEMS, and organic electronics. He has worked extensively in microfabrication-related areas such as plasma-source ion implantation, fabrication of microrelays and MEMS sensors, 3-D microelectronic circuits, and monolithic ferrite devices. His current research interests include the design and fabrication of microrelays, micromirrors, MEMS sensors, and nanoscale material properties and contacts. He directs the Microfabrication Laboratory and the Scanning Electron Microscopy Facility at Northeastern University. Dr. McGruer has contributed to the development of zero-power sensors, RF wake-up systems, and plasmonic microelectromechanical infrared digitizers, among other projects. He holds degrees in physics and electrical engineering from Michigan State University and has received awards such as the Søren Buus Outstanding Research Award and the Joel and Spira Excellence in Teaching Award.

Research topics

• Electrical engineering
• Engineering
• Composite material
• Optoelectronics
• Mechanics
• Mathematics
• Materials science
• Physics
• Optics
• Geometry

Selected publications

• Limitations on MEMS design resulting from random stress gradient variations in sputtered thin films

  Journal of Micromechanics and Microengineering · 2021 · 4 citations

  Senior authorCorresponding
  • Materials science
  • Optics
  • Mechanics

  Abstract Residual stress gradients often negatively affect the performance of MEMS devices, causing film curvature and changing the designed gaps of released structures. In this work, we built folded beams designed to compensate for the film curvature and keep the actuator gaps of sensitive resonant switches constant. While the average stress gradient is cancelled by our designs, we find that random variations in the stress gradient (rather than random variations in device dimensions) cause the majority of the observed variation in actuator gap. To our knowledge, this has not previously been reported, and represents an important limitation on MEMS designs using sputtered films. The standard deviation of the 400 nm contact gap for a folded beam of total length 152 µ m and width 108 µ m was measured to be about 134 nm. Using parameters measured from test cantilevers, our simulations predict that about 98% of the variation in contact gap is due to stress gradient variation, rather than variations in device geometry.

  PublisherDOI

• Zero-Power Acoustic Wake-Up Receiver Based on DMUT Transmitter, PMUTS Arrays Receivers and MEMS Switches for Intrabody Links

  2019-06-01 · 15 citations

  article

  This paper demonstrates, for the first time, a zero-power acoustic wake-up receiver for intrabody links, allowing Implanted Medical Devices (IMDs) to minimize the IDLE power consumption. This architecture is based on Directly Modulated Ultrasonic Transducers (dMUT) made of Lead Zirconate Titanate (PZT) as transmitter (TX), a Piezoelectric Micro Machined Ultrasonic Transducer (pMUT) array as receiver (RX), and a Micro Electro-Mechanical System (MEMS) switch. The role of the dMUTs and the pMUT array is to establish an acoustic link sensitive to signals as low as 50mV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> peak-peak at a distance of 10cm. This low signal triggers the switch which will turn on the IMDs from an IDLE-state to a full power mode.

  PublisherDOI

• Zero-Power Electrically Tunable Micromechanical Photoswitches

  IEEE Sensors Journal · 2018-06-27 · 25 citations

  article

  Micromechanical photoswitches (MPs) have shown orders of magnitude lower standby power consumption compared to their solid-state technology-based counterparts. In this paper, we demonstrate that the infrared detection threshold (i.e., the lowest detectable power of incident infrared radiation) of this new type of photoswitch can be effectively decreased by applying a bias voltage across the switch without compromising its key feature of near-zero standby power consumption and low false-alarm rate. We show that by exploiting the electrostatic pull-in effect (using bias voltage of ~7 V), a threshold as low as 76 nW can be achieved, which is the lowest threshold demonstrated to date for MPs. A mathematical model predicting the device threshold under a bias voltage is derived and verified by experiments. Furthermore, the effects of the bias on the device's stability are carefully studied suggesting the existence of a tradeoff between the detection threshold and the false-alarm rate when the bias is higher than 85% of the pull-in voltage. The source of the instability that causes false alarms is found to originate from charge accumulation over time in the dielectric substrate surrounding the bottom contact, which we believe can be mitigated by an improved contact design. Another effect associated with high bias is the contact stiction after infrared-triggered pull-in. To address this, a microheater is integrated into the switch to reopen the contacts while consuming only ~0.5 μJ per operation. This paper thus presents an effective solution for post-fabrication threshold adjustment of MPs, which is useful for applications requiring variable thresholds.

  PublisherDOI

• BROADBAND LONG-WAVELENGTH INFRARED MICROMECHANICAL PHOTOSWITCH FOR ZERO-POWER HUMAN DETECTION

  2018 Solid-State, Actuators, and Microsystems Workshop Technical Digest · 2018-05-21 · 6 citations

  articleOpen access

  This paper reports on the first demonstration of a longwavelength infrared (LWIR) micromechanical photoswitch (MP) suitable for human detection with zero-power consumption in standby. The proposed MP employs a highly-efficient broadband IR absorber (~80%, =8-12m), spectrally matching with the IR radiance of a human body. An ultra-low detection threshold of ~140 nW is experimentally demonstrated for the first time thanks to the high thermal sensitivity (~1.44 nm/nW) and stiffness (~0.033 nN/nm) of the optimized bimaterial actuating beams and the aggressively scaled nanoscale contact gap (<200 nm) maintained by the built-in temperature and stress compensation mechanisms. Such low threshold potentially enables human detection with a lens at a projected distance of 5.7 m.

  PublisherOA PDFDOI

• 750 MHZ ZERO-POWER MEMS-BASED WAKE-UP RECEIVER WITH -60 DBM SENSITIVITY

  2018 Solid-State, Actuators, and Microsystems Workshop Technical Digest · 2018-05-21 · 6 citations

  articleOpen access

  In this work, we present the first fully-passive RF wake-up receiver (WUR). The WUR relies on a solid-state envelope detector (ED) and a MEMS-based cantilever switch (RS) acting as a resonant comparator vibrating at 75.3 kHz. The device exhibits a quality factor (Q) of 4700 when operating in its linear regime (i.e. far from pull-in voltage). The demonstrated WUR enables the achievement of high sensitivity (P min =-60 dBm) while not consuming any standby power. For this reason, the presented WUR opens up exciting scenarios in the development of next-generation smart wireless sensors nodes operating within the Internet-Of-Things (IoT).

  PublisherDOI

• Design and Fabrication of an Electrostatic AlN RF MEMS Switch for Near-Zero Power RF Wake-Up Receivers

  IEEE Sensors Journal · 2018-07-27 · 14 citations

  articleSenior author

  We describe an aluminum nitride (AlN)-based resonant switch for use in a near zero power radio frequency (RF) wake-up receiver. A folded beam structure with a slot compensates for the curvature caused by the stress gradient in the sputtered AlN film and ensures that the released contact gap is approximately equal to the designed contact gap. A 80 kHz resoswitch with a Q of 8600 and an actuation gap of approximately 600 nm turns on when a -4 dBm, 800 MHz signal, square wave modulated at 80 kHz, is applied to the actuator. This AlN electrostatic resonant switch is designed to enable integration with a high gain AlN RF piezoelectric transformer to form a complete ultra-low power RF receiver.

  PublisherDOI

• A False Alarm-Free Zero-Power Micromechanical Photoswitch

  2018-10-01 · 3 citations

  article

  Zero-power infrared (IR) sensors based on Plasmonically-enhanced Micromechanical Photoswitches (PMPs) have recently been demonstrated, showing the capability to detect IR signatures with near-zero standby power consumption. However, current prototypes fail to discriminate between a targeted IR source (e.g. a flame) and a spurious one (e.g. an exhaust plume) having overlapping IR emission wavelengths, potentially getting triggered ON in the presence of strong interference and creating false alarms. This paper reports on the first experimental demonstration of a PMP augmented with an integrated passive false-alarm prevention mechanism to effectively desensitize it to spurious IR sources while maintaining a small footprint and near-zero standby power consumption. By incorporating two different narrowband plasmonic absorbers on a PMP - one tuned to the targeted IR wavelength and the other to a spurious wavelength - we show that the electrical contacts close in response to IR radiation at the targeted wavelength and remain open in the presence of spurious wavelengths, thereby preventing false alarms. Such an enhanced PMP prototype targeting flame detection with a threshold ~600 nW (minimum detectable IR power) is demonstrated showing zero false alarm to interfering IR sources. The increased reliability enabled by this technique makes PMP technology an ideal candidate for the implementation of large-scale maintenance-free wireless sensor networks with unlimited battery lifetimes.

  PublisherDOI

• MEMS-based near-zero power infrared wireless sensor node

  2018-01-01 · 27 citations

  article

  This paper reports on the first demonstration of an infrared (IR) wireless sensor node (WSN) with near-zero standby power consumption. The prototype presented here employs a plasmonically-enhanced micromechanical photoswitch (PMP) that exploits the energy contained in the impinging IR spectral band of interest itself, to perform passive sensing and digitizing functions. The palm-sized IR WSN demonstrated in this work comprises a vacuum-packaged PMP (IR power threshold ~284 nW, lithographically-defined IR absorptance: ~89% at 4.6 μm, 0.75 μm bandwidth) connected to a CMOS load-switch which wakes up a coin battery-powered sub 1-GHz wireless microcontroller to transmit data when the IR signal of interest is detected. The standby power consumption for the IR WSN was measured to be just ~2.6 nW: a >1900X improvement over state-of-the-art pyroelectric IR WSNs, while offering integrated spectral-selectivity. This work represents the first demonstration of an OFF-but-alert WSN that awakens only in the presence of a signal of interest, resulting in near-unlimited battery-life when deployed to detect infrequent but time-critical events.

  PublisherDOI

• Microelectromechanical detector of infrared spectral signatures with near-zero standby power consumption

  2017-06-01 · 16 citations

  article

  This paper reports the first experimental demonstration of a near-zero power (<;1 pW standby power consumption) detector of infrared (IR) spectral signatures. The proposed passive digitizer of IR spectral signatures is composed of 2 Plasmonically-enhanced MEMS Relays (PMRs) implementing a logic circuit. Unlike solid-state photodetectors, the PMRs exploit a plasmonically-enhanced thermomechanical coupling to selectively harvest the energy contained in an IR spectral band of interest itself and use it to mechanically create a conducting channel between the battery and the load without consuming any power in standby (i.e. while in the OFF state). In this work, we demonstrate for the first time, that by connecting in series 2 PMRs, tuned to different spectral bands (i.e. 4.1 μm and 5.6 μm), it is possible to implement a passive logic circuit capable of producing an output voltage (i.e. a quantized output bit that wakes up the active wireless sensor) only when exposed to the IR spectral signature associated to a target of interest (i.e. the exhaust plume of a vehicle). The event-driven sensing capability enabled by such a micro-scale IR digitizer can dramatically extend the battery life of wireless sensor nodes remotely deployed to detect infrequent but time critical events.

  PublisherDOI

• A microelectromechanical AlN resoswitch for RF receiver application

  2017-06-01 · 13 citations

  articleSenior author

  Resonant switches (resoswitches) using a novel design and fabrication process are reported. A folded beam structure compensates for the stress-gradient-induced bending in the sputtered AlN material and ensures that the free end of the center actuated beam is in plane with the anchor beams. A 21.14 kHz resoswitch with a Q of over 2000 and an actuation gap of 1.3 μm is turned on at the resonant frequency with a 0.5 dBm 800 MHz carrier that is square wave modulated at 21.14 kHz. This demonstration shows the feasibility of monolithically integrating a high gain RF piezoelectric transformer with a high-Q electrostatic resoswitch for a zero stand-by power RF wake-up receiver.

  PublisherDOI

Frequent coauthors

• George G. Adams

  Northeastern University

  63 shared

• Matteo Rinaldi

  Scuola Normale Superiore

  19 shared

• P.M. Zavracky

  Northeastern University

  18 shared

• Zhenyun Qian

  15 shared

• J. Krim

  North Carolina State University

  15 shared

• Sungho Kang

  Yonsei University

  14 shared

• Vageeswar Rajaram

  Northeastern University

  14 shared

• Cristian Cassella

  Universidad del Noreste

  13 shared

Labs

• Northeastern University College of Engineering Microfabrication LaboratoryPI

Awards & honors

• Søren Buus Outstanding Research Award, College of Engineerin…
• Joel and Spira Excellence in Teaching Award
• Patent for Zero Power Sensors
• Patent for Zero Power Radio Frequency Receiver
• Patent for Directed assembly of carbon nanotubes and nanopar…