A stainless-steel-based implantable pressure sensor chip and its integration by microwelding

Significance Statement

Micromachined pressure sensors based on micro-electro-mechanical-systems (MEMS) technology are commonly used in a range of applications including medicine, aviation, and electronics. A capacitive transducer is a major form of the micro-electro-mechanical-systems and has several benefits over the piezo-resistive sensors, which include small temperature drift, high resistance to packaging stress, high sensitivity, and low power consumption.

MEMS sensors have been developed by implementing stainless steel for applications in biomedical and harsh environment applications. In the latter application, the silicon die of the sensor is normally encapsulated in a robust housing and sealed by a protective diaphragm, which are both made of corrosion resistant as well as high fracture strength stainless steel. This packaging comes with increased manufacturing cost and alteration in the sensing behavior after packaging.

There have been developed studies to construct capacitive pressure sensors with the sensing diaphragm and the substrate directly out of stainless steel in a bid to eliminate the need for additional packaging, therefore, avoiding the stated problems. Stainless steel-based sensors exhibit superior robustness against high pressures as well as corrosive media. However, this comes at a cost of pressure sensitivity that is caused by the high stiffness of the diaphragms. Therefore, to address this concern, there is a need to use other stainless steel-based capacitive pressure sensors that encompass non-stainless steel diaphragm.

Researchers led by Professor Kenichi Takahata at The University of British Columbia in Vancouver developed a capacitive gauge pressure sensor that was built on the bulk-micro machined medical-grade chip with a gold-covered sensing diaphragm. The diaphragm was to offer chemical robustness as well as biocompatibility. For the sensor design, the authors analyzed the incorporation of dead-end hole structures in the reference cavity for its advantage in improving sensors sensitivity. Their work is published in Sensors and Actuators A: Physical.

The authors developed a 1.5×1.5 mm2 stainless-steel chip of capacitive pressure sensor as well as its integration method with an aim on smart implant applications. They entirely micro fabricated the sensors with biocompatible materials via thermal bonding of gold-polyimide diaphragm film to the chip dies, which were made of medical-grade stainless steel. They verified the reference cavity design with dead-end holes made in the stainless steel die both experimentally and theoretically in order to improve pressure sensitivity. The authors also investigated laser micro welding as a substitute path for this form of stainless steel-based sensors. This was in a bid to establish a permanent and reliable bond onto stainless steel platform gadgets.

As expected from theoretical analysis, the presence of dead-end holes inside the air-sealed reference cavity was confirmed experimentally to improve the sensor’s sensitivity. The authors observed that the fabricated sensors exhibited an average sensitivity of about 100 ppm/mmHg over an average gauge pressure of 250 mmHg. The sensors were laser micro welded to the stainless steel substrates and indicated no considerable alteration of their sensing capability after welding. The welding process was observed to provide mechanical as well as electrical advantage over the typical conductive epoxy bonding.

The sensor incorporation through micro welding was as well shown on stainless steel stents and hypodermic needle, as an initial path towards its implementation to developing smart devices with a pressure monitoring capability. Therefore, laser micro welding is a promising method for packaging developed sensors and a number of micro-devices based on stainless steel materials.

A stainless-steel-based implantable pressure sensor chip and its integration by microwelding-Advances in Engineering

About The Author

Xing Chen received the B.S. degree in mechanical engineering from Kunming University of Science and Technology, Yunnan, China, in 2004, and his M.S. and Ph.D. degrees in mechanical system engineering from Chonnam National University, Gwangju, Korea, in 2008 and 2012, respectively. From 2012 to 2014, he was a Post-Doctoral Research Fellow with the Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, Canada.

He is currently a Research Associate with the Department of Anesthesiology and Critical Care Medicine, Johns Hopkins School of Medicine, Baltimore, USA. His research interests include microactuators, microsensors based on graphene and stainless steel, scanning probe microscopy, and implantable biomedical microdevices.

About The Author

Daniel Brox received B.Sc. and M.Sc. degrees in mathematical physics and mathematics in 2005 from the University of British Columbia, Vancouver, Canada. In 2008 he received an M.Sc. degree in electrical engineering from the California Institute of Technology, Los Angeles, California. He received the Ph.D. degree in electrical and computer engineering at the University of British Columbia in 2014, with a focus on implantable MEMS-based devices with wireless blood pressure monitoring capability.

About The Author

Babak Assadsangabi received the B.Sc. and M.Sc. degrees in mechanical engineering from Shiraz University, Shiraz, Iran, in 2006 and 2009, respectively and he got his Ph.D. in electrical and Computer engineering at the University of British Columbia, Vancouver, Canada, in 2014. He is currently holding a Post-Doctoral position at the University of British Columbia. His research interests include Ferrofluid-based microactuators and sensors, magnetic MEMS, and implantable microdevices.

About The Author

Mohamed Sultan Mohamed Ali received the B.Eng. and M.Eng. degrees in electrical engineering from Universiti Teknologi Malaysia, Skudai, Malaysia, in 2006 and 2008, respectively, and the Ph.D. degree in electrical and computer engineering from the Department of Electrical and Computer Engineering, The University of British Columbia, Vancouver, BC, Canada, in 2012. From 2001 to 2007, he held various engineering positions at Flextronics International Ltd. and Jabil Circuit, Inc. He is currently a Senior Lecturer with the Faculty of Electrical Engineering, Universiti Teknologi Malaysia.

Dr. Mohamed Sultan also serving as consultant for Flextronics Malaysia in failure analysis division and actively involved in many industrial projects. Dr. Mohamed Sultan has published over 60 technical papers in MEMS and relate fields. He has also served as the editor of 3 books in Mechatronics. His research interests are in the areas of MEMS, nanotechnology, and micro/nanofabrication technologies, including wireless microdevices, integration of microstructures, and microrobotics.

About The Author

Kenichi Takahata received the B.S. degree in physics from Sophia University, Tokyo, Japan, in 1990 and the M.S. and Ph.D. degrees in electrical engineering from the University of Michigan, Ann Arbor, in 2004 and 2005, respectively. He is currently an Associate Professor in the Department of Electrical and Computer Engineering at the University of British Columbia, Vancouver, Canada, as well as a Canada Research Chair in Advanced Micro/Nanofabrication and MEMS. He joined Matsushita Research Institute Tokyo, Inc. in 1990 and was with Matsushita Electric Industrial Co., Japan, until 2001 (both presently Panasonic). From 1999 through 2001, he held a Visiting Scientist position at the University of Wisconsin, Madison.

He was a Senior Research Engineer with the Corporate Research Laboratory at 3M Company, St. Paul, USA from 2005 to 2006. He joined the University of British Columbia as an Assistant Professor in 2006. Dr. Takahata has published over 100 papers in micro/nanofabrication, MEMS, and related fields and holds 11 issued patents.

He served on technical committees of various conferences, including the IEEE International Conference on Micro Electro Mechanical Systems, the IEEE Sensors, and the International Conference on Solid-State Sensors, Actuators and Microsystems (Transducers) where he serves on the International Steering Committee. He is part of the editorial boards of the IET Electronics Letters and the Frontiers for its M/NEMS section, and currently serving as a guest editor for Journal of Micromechanics and Microengineering.

He also served as the editor of two books in MEMS. His research interests are in the areas of MEMS, nanotechnology, and micro/nanomanufacturing, including wireless microdevices, bioMEMS, integration of nanomaterials and microstructures, and microplasma control and application.

Reference

Xing Chen, Daniel Brox, Babak Assadsangabi, Mohamed Sultan Mohamed Ali, and Kenichi Takahata. A stainless-steel-based implantable pressure sensor chip and its integration by micro welding. Sensors and Actuators A, volume 257 (2017), pages 134–144.

Go To Sensors and Actuators A