As the largest foundry in Malaysia, SilTerra has been developing its MEMS-on-CMOS platform and expanding it into new applications such as PMUTs for medical and fingerprint sensors, SAWs for timing devices, and BAWs for short range wireless RF transceivers. The company works with clients on basic proof of concepts, custom device prototype development, manufacturability assessments and volume production. We recently spoke with Arjun Kumar Kantimahanti, Senior Vice President of SilTerra’s MEMS, Sensors, and Life Sciences Business Unit. In this detailed interview, we discuss SilTerra's history, it's current MEMS program, as well as it's roadmap and plans for the future. We also spoke about emerging applications enabled by optical, RF, and ultrasonic MEMS devices.
MEMS Journal: What’s the history of MEMS at SilTerra and how did your capabilities evolve over the years?
Arjun Kumar: The history of MEMS at SilTerra started in the year 2010. Our first development project for MEMS was a micro-mirror array device for a display chip used in data projectors. We integrated this MEMS device over our 0.18 micron CMOS technology. We developed a manufacturable process and achieved repeatable yield performance. The first device is a customer proprietary device, 1 MPixel WXGA.
Subsequently, in the year 2011 we started to develop our MEMS-on-CMOS device architecture to set up the platform for RF MEMS integrated solutions. Resonator devices fabricated on our platform cover a wide spectrum of reference frequencies ranging from 10 MHz to 2.4 GHz. We also started the ultrasonic MEMS program in 2015 to address the growing needs in the finger-print sensing and medical imaging market segments.
MEMS Journal: Why did you start offering MEMS foundry service capabilities?
Arjun Kumar: SilTerra is primarily a CMOS foundry offering advanced logic/BCD/RF CMOS and we started our MEMS program to complement the existing portfolio with add-on MEMS modules to enhance product functionality.
MEMS Journal: What’s the vision for SilTerra as well as its MEMS business? How do you see SilTerra and its MEMS business five years from now?
Arjun Kumar: Our vision is to offer a mature MEMS-on-CMOS platform so that it could support various MEMS devices and sensors that are critical for the upcoming markets such as IoT and autonomous vehicles. We will also continue to support customer-driven processes through our MEMS foundry service model. SilTerra is targeting to derive 20% of its revenue from MEMS market within 5 years from now.
MEMS Journal: What are your core strengths, as compared to other MEMS foundries? What can you do better than other MEMS foundries?
Arjun Kumar: Our unique strength is the simplicity of our MEMS-on-CMOS platform and our ability to build various MEMS devices on pre-processed CMOS wafers.
Additionally, we produce complex chips for photonics and bio-photonics applications and these chips use process modules that are very similar to MEMS devices thus allowing us to go through the yield and reliability learning curve. We also use defect density monitoring test structures to continuously improve our yield.
We also develop manufacturable process modules for customer specific device architectures to validate their proof of concept and build capacity to support their volume requirements.
MEMS Journal: Which new MEMS processes have you added recently? Which new MEMS tools did you install recently?
Arjun Kumar: Our latest release is the PMUT process which can be built either on our 180nm or 130nm platform. Probably we are one among the first to offer monolithic PMUT fabrication service. Recently, we added a “release tool” and we are in the process of acquiring a second piezoelectric deposition tool.
MEMS Journal: What are your expansion or upgrade plans? What’s on your technology and process development roadmap for the next 1-2 years?
Arjun Kumar: We are going to add process modules for high aspect ratio silicon etch for microfluidic applications and cavity SOI-based PMUT platforms for industrial sensors.
MEMS Journal: Which types of MEMS devices have you fabricated in your fab so far? How many wafers do you currently run per month?
Arjun Kumar: Optical MEMS (micro-mirror array chips), RF MEMS (electrostatic resonators, surface acoustic wave resonators, and bulk acoustic wave resonators), ultrasonic MEMS (PMUTs), and MEMS motion sensors (accelerometers). Our installed 8-inch capacity for MEMS is 3,000 wafers per month, complemented by our CMOS installed capacity of 40,000 wafers per month. Our MEMS capacity ramp is planned to be in line with MEMS products acceptance in the market.
MEMS Journal: How do you develop integrated MEMS solutions? Who are some of your partners and how do you work with them?
Arjun Kumar: Building integrated MEMS devices is quite challenging. We worked on this integration and its manufacturability for more than 5 years and developed a few innovative process modules that allow the seamless integration with ASIC wafers. In order to offer a complete solution (not just wafer processing), we collaborate with IC design experts, R&D organizations, academic institutions, and semiconductor assembly plants across the world. Our team is focused on offering solutions towards specific markets such as timing, radio frequency, and imaging.
MEMS Journal: What’s your main focus related to timing applications? What kinds of frequencies and use cases are you pursuing first?
Arjun Kumar: Main focus is to provide a monolithic reference oscillator using our thin film acoustic resonator technology. We have collaborated with our partner and demonstrated reference clock at 320 MHz with an integrated phase jitter of 160 fs (12 kHz to 20 MHz) The targeted product is a programmable acoustic oscillator (AO) for consumer and automotive applications.
MEMS Journal: Which types of RF MEMS applications are you pursuing?
Arjun Kumar: We have demonstrated a high frequency oscillator (QFN packaged FBAR oscillator at 2.4GHz with an integrated phase jitter of 358 fs). We are working on integrated high frequency RF transceivers.
MEMS Journal: What are some of the most interesting MEMS based imaging applications that you are seeing right now?
Arjun Kumar: PMUT is emerging for the portable medical imaging applications, gesture control, and finger print sensing.
MEMS Journal: What are the latest trends with fingerprint sensors?
Arjun Kumar: Latest trend is to mount the finger print sensors under the glass display screen, PMUT technology is compatible with under the glass sensing and highly secured against fake finger prints. SilTerra’s PMUT on CMOS will be an interesting tool kit for the designers in this field
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