MEMS technology is inevitable for ultrasound devices such as BAW filters, pMUT and cMUT. In this short course, the lecturers, who have been deeply involved in developing both MEMS and ultrasound device technologies, present and discuss the following MEMS-related fabrication and design techniques for the ultrasonics community:
1. MEMS fabrication technology and process integration - Fundamental concepts learned from historical papers
2. Modern MEMS processes used for mass-production
3. Multi-frequency contour-mode resonator design and fabrication
4. GHz frequency ultrasonic resonant actuators
MEMS fabrication technology is based on semiconductor manufacturing technology, but there are varieties of MEMS-specials, which you should know for the process integration of MEMS. In the first half of this lecture, Prof. Tanaka will explain “beautiful” examples of MEMS process picked up from historical papers, and then modern MEMS processes used for mass-production. Through a plenty of examples, you will be taught what is MEMSwise thinking in the design and process integration. The goal of this part is to augment options of process technology applicable for your ultrasonic devices.
In the second half of this short course, Prof. Bhave will cover the design and fabrication of contour mode resonators, discuss their scaling to GHz frequencies and compare and contrast them to the mass-produced and industry-leading film bulk acoustic resonators (FBAR). In the last hour, we will segway into a brief discussion of high overtone bulk acoustic resonator (HBAR) design and introduce how these “old” resonators are finding new applications in communication, computing, photonic and quantum systems.
This short course is different from one in the last year, and worth taking also for who took the last years’ short course about MEMS technology.
Sensor is an essential application for acoustic wave devices. The first sensor based on a quartz crystal resonator was proposed by G. Sauerbrey in 1959. Furthermore, Wohltjen and co-workers proposed a gas sensor using surface acoustic wave (SAW) devices in 1979. Moreover, International Standards for piezoelectric sensors, including the acoustic wave-based sensors, were published in 2017. The acoustic wave-based sensors are grouped into three categorize, including physical, chemical, and biochemical sensors. The chemical and biochemical sensors require a sensitive or receptive layer as target recognition material. However, this layer is no needed for the physical sensor. In the short course, we focus on the shear horizontal surface acoustic wave sensor (SH-SAW) for the liquid environment. For knowing the detection mechanism, it is necessary to understand the change of field distributions of particle displacements and potential. Therefore, the penetration depth is important information for the liquid-phase sensor. The changes in the penetration depth influence the SH-SAW sensor response. Furthermore, the penetration depth is an inverse proportional to the frequency, so considering the penetration depth is essential for the optimization of the sensor frequency. Finally, the short course covers the following topics. 1) Fundamentals of acoustic wave-based sensors 2) Numerical calculation method of SH-SAW at liquid/solid interface 3) Fundamentals of perturbation theory for SAW sensors 4) Field distributions of particle displacements and potential in liquid 5) Applications of SAW sensors
The organizers gratefully acknowledge the generous support provided by the following