Microsystem technologies for implantable applications

Microsystem technologies (MST) have become the basis of a large industry. The advantages of MST compared to other technologies provide opportunities for application in implantable biomedical devices. This paper presents a general and broad literature review of MST for implantable applications focused on the technical domain. A classification scheme is introduced to order the examples, basic technological building blocks relevant for implantable applications are described and finally a case study on the role of microsystems for one clinical condition is presented. We observe that the microfabricated parts span a wide range for implantable applications in various clinical areas. There are 94 active and 67 commercial 'end items' out of a total of 142. End item refers to the total concept, of which the microsystem may only be a part. From the 105 active end items 18 (13% of total number of end items) are classified as products. From these 18 products, there are only two for chronic use. The number of active end items in clinical, animal and proto phase for chronic use is 17, 13 and 20, respectively. The average year of first publication of chronic end items that are still in the animal or clinical phase is 1994 (n ≤ 7) and 1993 (n ≤ 11), respectively. The major technology-market combinations are sensors for cardiovascular, drug delivery for drug delivery and electrodes for neurology and ophthalmology. Together these form 51% of all end items. Pressure sensors form the majority of sensors and there is just one product (considered to be an implantable microsystem) in the neurological area. Micro-machined ceramic packages, glass sealed packages and polymer encapsulations are used. Glass to metal seals are used for feedthroughs. Interconnection techniques such as flip chip, wirebonding or conductive epoxy as used in the semiconductor packaging and assembly industry are also used for manufacturing of implantable devices. Coatings are polymers or metal. As an alternative to implantable primary batteries, rechargeable batteries were introduced or concepts in which energy is provided from the outside based on inductive coupling. Long-term developments aiming at autonomous power are, for example, based on electrostatic conversion of mechanical vibrations. Communication with the implantable device is usually done using an inductive link. A large range of materials commonly used in microfabrication are also used for implantable microsystems. © 2007 IOP Publishing Ltd

Wafer level hermetic package and device testing of a SOI-MEMS switch for biomedical applications

We have designed a wafer level chip scale package for a bi-stable SOI-MEMS dc switch using a silicon-glass hermetic seal with through the lid feedthroughs. Bonded at 365 °C, 230 V and 250 kg, they pass the fine/gross leak test after thermal cycling and mechanical shock/vibration according to MIL-STD-833, fulfilling the requirements for biomedical applications. The measured shear strength is 114 26 N in correspondence with the theoretically expected 100 N. Ruthenium microcontacts are a factor of 100 more robust than gold microcontacts, being stable over 106 cycles measured in a N2 atmosphere inside the package presented here. Future work will include a more extensive bond quality assessment and continued microcontact reliability measurements. © 2006 IOP Publishing Ltd

Laterally Moving Bistable MEMS DC Switch for Biomedical Applications

In this paper, we have designed a bistable microelectromechanical switch for an implantable lead electrode multiplexer application. Fabrication is based on a single mask process. State changes require an 18 V pulse to the actuators consuming only 0.2 nJ energy. The switch does not consume any energy in either the ON or the OFF state. Total chip size including bond pads is approximately 1.5 mm × 1.5 mm. The initial contact resistance is below 5 Ω with a contact force in the order of 10 μN. The contact resistance stays consistently below 30 Ω for the first 40 000 cycles. Breakdown voltage between the two contact members in OFF state is 300 V. We plan to further investigate applicability of this switch in the biomedical field. © 2005 IEEE