Graduate Research Assistant, Columbia University
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Abstract
3D Monolithic Integration of Piezoelectric MEMS on CMOS for RF and Sensing Applications
Radio frequency and wireless systems require high quality passive components, capacitors and inductors (LC), for the implementation of highly selective filters and stable reference oscillators. CMOS technology offers a low cost versatile platform widely used in analog and digital systems but it falls short when it comes to high frequency (>1GHz) applications as a result of its lossy on-chip passives. Piezoelectric microelectromechanical (MEMS) passives show lower electrical losses than LC because their signal processing happens in the mechanical domain. Developing a CMOS compatible process for the monolithic integration of these devices with the underlying circuitry will allow circuit designers to test new wireless system topologies for software cognitive radios and multiband processing. A CMOS chip was designed and taped-out for the development of this project. The process flow developed and a working device on-chip are shown in this work.
These acoustic devices can be also be used as sensors, which are sensitive to temperature and mass changes. By adding susceptive layers or absorber coatings these structures can be functionalized to detect infrared (IR),ultraviolet (UV) wavelengths or for volatile organic compound (VOC) gas detection. Their selectivity and sensitivity will be determined by the coating and frequency, respectively. Results for both sensor types are shown in this work.
Bio
I was born and raised in Puerto Rico and went to the University of Puerto Rico Mayaguez Campus where I graduated in May 2013 with my bachelor’s degree in Electrical Engineering. During my undergrad years I had the chance to work on different research topics and quickly developed an interest for interdisciplinary research. I worked with Dr. Nayda Santiago on developing an algorithm on FPGAs for hyperspectral imaging for anomaly detection that could be used for defense (missile detection). I also worked with Dr. Guillermo Serrano on the design and layout of a thermal energy harvesting circuit using dc-dc converters avoiding the use of inductors by adding switch capacitors and lowering area cost and towards the end I built and programmed test benches for all of the taped-out ICs. For my senior design I had the opportunity to be the program manager for a group of people with diverse academic backgrounds (electrical engineering, computer engineering, biotechnology, agriculture and mechanical engineering), where we designed and built a self-sustained smart vertical garden. We used solar energy as our main power source and were able to control when the lights and water would come on through Bluetooth and a phone application. I did two summer internships one at the National Institute of Standards and Technology (NIST), automating femto- to nano- current measurements for calibration systems, and one in UC Berkeley, studying and fabricating organic gravure printed solar cells. I enjoyed working and learning about different areas during my undergrad and I knew I wanted to work on an interdisciplinary or a system project for my grad school project.
In August 2013 I started my Masters/PhD program at Columbia University with Dr. Ioannis Kymissis as my advisor. Knowing of my interest for systems he assigned me a partner for the first two years to work on the fabrication and integration of piezoelectric micro electromechanical systems (MEMS) with CMOS integrated circuits (IC).The first two years I spent fabricating different structures on glass and characterizing them up to the point of extracting an electrical model that I later on used for the design of an IC. We were able to successfully develop a die-friendly fabrication process and using the on chip circuit measured the output of the MEMS–CMOS oscillator. After publishing these results I moved on to studying different materials that can be used with our structure for mass or temperature sensing (piezoelectric materials change their resonance frequency in response to mass loading or thermal change). During the first summer as a grad student I did an internship at IBM-Tokyo, working on optical interconnects and how to improve communication from chip to board using micro-lens. I graduated in 2015 with my master’s degree in Electrical Engineering from Columbia University. I am currently working on a new IC for multi-sensing capabilities using our structures and functionalizing the surface with different materials for IR (thermal), gas and liquid (mass) sensing.