The piezoelectric blessing is bestowed upon many MEMS devices – An interview with Robert Bosch

Courtesy of Bosch - MEMS, Mobility

In a turbulent global economic environment, MEMS shows promising growth. According to Yole Développement (Yole) “Status of the MEMS Industry 2019” report, the market will exhibit +8.3% growth in value in the period 2019 – 2024, reaching US$18.5 billion in 2024. Consumer still has the biggest share with more than 60% of the total market and with automotive following up: almost 20% of the total market.

Piezoelectric technology is increasing its momentum in MEMS markets. More and more gyroscopes, BAW filters, and inkjet heads are being developed using this technology, and now microphones, microspeakers, autofocus, and pMUT (for fingerprint sensors, ultrasound, and gesture recognition) are also underway. Furthermore, several MEMS foundries have already integrated a piezo process (PZT, AlN) in their fabs. In total, it is a more than $6B thin-film piezo based device market in 2024 that Yole forecasts in its “Piezoelectric Devices: From Bulk to Thin Film 2019” report, a market opportunity with technological challenges and choices for MEMS fab and foundries.

In this context, Jérôme Mouly, Senior Technology & Market Analyst and Dimitrios Damianos, PhD., Technology & Market Analyst, both at Yole have interviewed Dr. Udo-Martin Gómez, Senior Vice President at Robert Bosch, an industry leader in both the consumer and automotive MEMS markets, who also has piezoelectric MEMS manufacturing capabilities.

Jérôme Mouly (JM): Could you please introduce yourself to our readers? What are your responsibilities at Bosch?           

Dr. Udo-Martin Gómez (UMG): My name is Udo Gómez and I am head of the MEMS sensor development and Sensor Business Line at Bosch’s Automotive Electronics business unit. The main focus of our business is the provision of new technologies for MEMS high-volume production and the development and marketing of innovative MEMS sensors for numerous automotive applications.

JM: Bosch is a major MEMS player with production capability of more than 3000 wafer starts per day. The company is now also offering foundry services for custom projects. What are Bosch’s motivations to provide open foundry services?

UMG: We are currently enlarging our 200mm production capabilities for MEMS.  Therefore, we want to increase and broaden our MEMS business, for example by providing MEMS for markets which are not traditional Bosch markets, namely by increasing foundry service for new customers. For over 12 years Bosch has provided MEMS foundry services for Silicon Valley based company SiTime, which is a market leader in MEMS-based timing devices. Our goal is to put our customer in a position to enter new markets successfully or boost existing business by providing next generation technology. We strive for a win-win long term partnership as a reliable and stable foundry supplier.

JM: Could you tell our readers what Bosch’s foundry capabilities are: technology portfolio, manufacturing capability…?      

UMG: Bosch can accelerate customer specific development due to the availability of the probably broadest technology portfolio among MEMS suppliers, as shown below. We offer our customers flexible R&D willingness and capabilities, a huge know-how in MEMS based on decades of experience, and finally a highly professional production capability with respect to quality, reliability, high volumes, steep ramp-ups and long-term delivery guarantee.

Technology portfolio:

  • KrF Lithography for MEMS down to 130nm
  • All standard ASIC processes
  • Surface and Bulk micromachining
  • DRIE (Bosch Process)
  • Vapor phase etch with HF for silicon oxide and XeF2 for Si
  • KOH etch
  • TSV in silicon or metal
  • Anti stiction and ALD coatings
  • PZT, AlN
  • Bonding: Anodic, glass frit, eutectic AlGe and epi seal
  • Gas or vacuum sealing, reseal
  • SiRiN
  • Porous silicon
  • Backside alignment and processing
  • Grinding and polishing (esp. bonded wafer pair)

Manufacturing capabilities

  • Front-end
    1. 3 wafer fabs (150mm and 200mm)
    1. More than 3000 wafer starts per day
    1. All fabs qualified for automotive and consumer:
      1. IATF 16946
      1. ISO 14001
      1. and others
      1. Backend
  • Back-end
    • Wafer level test for 150mm and 200mm
    • Sensor assembly
    • Final test for packaged devices

Dimitrios Damianos (DD): Bosch’s foundry services include Piezoelectric MEMS production. What kind of piezo material and deposition technology are you using?

UMG: Yes, you are right. For several years we have been expanding our process and material portfolio. Regarding piezoelectric materials we’ve decided to introduce PZT and AlN in our MEMS fab. Both materials will be deposited onto 200mm wafer by Sputtering. We have state of the art equipment, e.g. we deposit PZT with an ULVAC sputter tool. And we are working together in JDPs (Joint Development Programs) to further improve the process, including integration aspects with respect to our application demands. For AlN we rely on a state of the art Sigma PVD tool from SPTS Technologies with a special feature for improved uniformity.

An example of an optical device showing the complexity of multiple wafers bonded and the huge variety of processes to be possessed – Courtesy of Robert Bosch

DD: Sputtering is a deposition technique. What are the benefits compared to other techniques, such as Sol-Gel? What are Bosch’s main achievements (thickness, uniformity…)?           

UMG: When we started the pre-development phase of piezoelectric MEMS, we made a thorough analysis of our application needs and compared this with the known deposition technologies, like Sol-Gel, PLD, Sputtering and others. In the end we decided on sputtering. Sputtering tools are well known in semiconductor fabs. The supply chain regarding sputter targets and other media is well established. This results in process and material properties which are under all circumstances controllable and reproducible even in high volume. Another advantage – regarding PZT – is the possibility to reduce the deposition temperature which gives us more flexibility in integrating the piezoelectric layer on top of the transducer.

Typical values:

  • PZT: e31: -12 …-14 C/m2; thickness range: 500 – 2000nm (depends on application), uniformity: < 10%
  • AlN: e31: ~ -1 C/m2, relative permittivity  ~ 10, thickness range: 200-1500nm, < 50MPa stress uniformity

DD: What kind of PiezoMEMS products could Bosch target with its Piezo offer?

UMG: From the material side we can provide our customers Piezo-based sensors and actuators. We are open to all relevant piezoelectric MEMS markets, like inkjet printheads, micro-mirrors, micro-speakers and transducers, ultrasound imaging for robotics or push-button replacement for smart phones and others. But of course, the implementation strongly depends on a reliable business model of our customer.

DD: In the market, how do you see interest in PiezoMEMS growing, and what are the advantages of Piezo-sensing capabilities?          

UMG: The variety of MEMS is increasing dramatically due to an increased penetration in existing as well as new markets. These include optical and medical applications, communication systems, household applications, IoT and I4.0. With increasing AI, the necessity of sensing and acting will also increase, resulting in more MEMS demand. And in all of those fields, AlN and PZT play their role.

The material of choice in piezo-sensing applications is AlN. The main advantages in addition to its CMOS compatibility and ease of integration is the low permittivity and dielectric loss. Those ideal material properties in combination with the miniaturization by MEMS technology may enable high resolution ultrasonic imaging on small devices and other use cases. You may know our other well established sensing technologies based on the capacitive or piezoresistive principle. Beside these principles the Piezo-sensing technology opens up a new field of applications. Each of the principles have their Pro’s and Con’s therefore the choice of a sensing principle strongly depends on the application requirements. For us it is important to widen our technology spectrum with an AlN process module to be able to address new customer demands.  

JM: Inkjet printheads, inertial MEMS and Filters are currently still growing markets. However, do you see any emerging PiezoMEMS devices?

UMG: The next big hype for PiezoMEMS may also arise from MEMS timing devices, ultrasonic transducers, vibrational energy harvester in I4.0 and others. The number of opportunities is immense.

JM: Would you like to mention anything else to our readers?

UMG: MEMS is an attractive growing market field with a lot of opportunities. Bosch, as a leading MEMS player, offers its expertise and manufacturing capabilities to innovative ideas of our customers to open up new markets in a fruitful and successful partnership.

Interviewee:

Dr. Udo-Martin Gómez is Senior Vice President of Robert Bosch GmbH. He heads the Sensors and Sensor Engineering Business line at Bosch’s Automotive Electronics business division in Reutlingen, Germany, the world’s largest MEMS sensor supplier serving the Automotive, Consumer Electronics and IoT industry.
Having completed his doctorate in physics, Dr. Gómez started his career at Robert Bosch GmbH in 1999 in Corporate Sector Research and Advanced Engineering (MEMS technology).
Before joining Automotive Electronics in April 2018, he worked in various management positions at Bosch and also held the position of Chief Expert for MEMS sensor technology. From 2013 to March 2018, he was Chief Technical Officer of Bosch Sensortec GmbH – a wholly owned subsidiary of Robert Bosch GmbH, responsible for research and development of micro-electro-mechanical sensors (MEMS) for consumer electronics, smartphones, security systems, industrial technology and logistics.
Since 2014, Dr. Gómez is member of the Board of VDE/VDI-Society Microelectronics, Microsystems and Precision Engineering (GMM). Since 2015, he is also member of the GSA (Global Semiconductor Alliance) EMEA Leadership Council.

Interviewers:

Dimitrios Damianos - Yole Développement

Dimitrios Damianos, PhD joined Yole Développement (Yole) as a Technology and Market Analyst and is working within the Photonics, Sensing & Display division. Dimitrios is daily working with his team to deliver valuable technology & market reports regarding the imaging industry including photonics & sensors.
After his research on theoretical and experimental quantum optics and laser light generation, Dimitrios pursued a Ph.D. in optical and electrical characterization of dielectric materials on silicon with applications in photovoltaics and image sensors, as well as SOI for microelectronics at Grenoble’s university (France).
In addition, Dimitrios holds a MSc degree in Photonics from the University of Patras (Greece). He has also authored and co-authored several scientific papers in international peer-reviewed journals.

Jérôme Mouly serves as a Senior Technology & Market Analyst & Business Developer specialized in microtechnologies for inkjet & bioMEMS sensors at Yole Développement (Yole). Jérôme is supporting the development of strategic projects, following leading customers of the company, within the Life Sciences & Healthcare division. Since 2000, he is also engaged in more than 100 marketing and technological analyses for industrial groups, start-ups and institutes related to semiconductor & medical technologies industry, in the field of inkjet functional printing, wearable sensors and connected medical devices. Jérôme is also regularly involved in international conferences, giving presentations and delivering keynotes. Jérôme Mouly holds a Master of Physics from the University of Lyon (France).

Related reports:

Piezoelectric Devices: From Bulk to Thin-Film 2019

How strongly will piezoelectric’s good vibrations resonate in the device market?

Status of the MEMS Industry 2019 - Yole Développement

Status of the MEMS Industry 2019

What does the future hold for the MEMS Industry?

Source: http://www.yole.fr, http://www.bosch.com

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