Ultrathin flexible hermetic encapsulation of mechanical sensors for long term electronic implants

Gent - PhD
More than two weeks ago

Be part of the development of highly advanced electronic implants by investigating flexible hermetic encapsulation techniques for mechanical sensors to be used as components for sensing or powering of long term implantable devices.

Recently, the use of microsystems for biomedical applications is getting more attention. Such microsystems consist of one or more chips, sensors, a battery, electrodes, etc. They are developed to be used on or close to the body, or even inside to body (so called in-vivo applications). In case of in-vivo use, a lot of extra measures have to be taken into account: the body has to carry the implant without harmful consequences, and moisture from the body should not penetrate into the implant, leading to corrosion resulting in failure of the microsystem. Hence a biocompatible and hermetic package is needed for such implantable systems. Traditionally, an implantable system is placed into a rigid Titanium box (See Fig. 1). Such box is indeed biocompatible and hermetic, offering the ‘safety’ of a well-known package for implants, but at the high price of large implantable devices with more patient discomfort and a higher risk on complications after implantation, such as a pronounced foreign body reaction or infections. The development of a novel miniaturized packaging technology for implants, optimized for patient comfort combined with excellent patient safety and device functionality, would offer important new possibilities to the medical world. 
pacemaker packaged in rigid Ti box
Fig. 1: pacemaker packaged in rigid Ti box, shown before and after implantation. The electrodes are located at the distal end of the lead. The main device in the Ti-box is implanted sub-cutaneous to allow signal transmission/ powering  by inductive coupling (one induction coil inside the device, the second one will be placed on the skin during signal transmission and charging), while the electrodes are positioned in the heart.
Within a collaboration between CMST (an Imec-associated lab at the UGent university) and Imec in Leuven, a considerable amount of research is performed to develop a very novel implantable packaging technology, in order to realize a very small, flexible, biomimetic package for electronic implants. All involved technology developments are part of our internal FITEP technology platform (FITEP: Flexible Implantable Thin Electronic Package). Important progress is made already in the packaging technology for implants having electrodes as sensors, as can be seen in Fig. 2. The device encapsulation consists of a multilayer of biocompatible polymers and ultrathin ceramic diffusion barriers deposited using ALD techniques (ALD: atomic layer deposition) in order to fabricate a very thin and flexible but also highly hermetic device packaging. Based on the successful results with this alternative device encapsulation, we would like to expand our research to optimized polymer/ALD encapsulation techniques for mechanical sensors such as pressure sensors or acoustic sensors, where moving or flexing parts form an extra challenge. A rigid Titanium box is certainly not a good packaging option for such sensors, while our flexible encapsulation methodology offers important advantages due to its limited thickness and flexibility. 
. Electronic chip and electrical wiring
Fig 2. Electronic chip and electrical wiring, fully packaged by CMST/imec’s ultrathin flexible hermetic encapsulation based on the FITEP technology platform. The total packaged chip is only 75nm thick and highly flexible as illustrated in the pictures. This flexibility makes this type of implantable package very interesting for mechanical sensors having moving/ flexing/ bending parts.
At imec, several novel mechanical sensors are developed which are very interesting for implantable devices, such as pressure sensors or acoustic sensors (so called CMUTs). A test chip containing imec’s new MOMS-based pressure sensor is shown in Fig. 3. For various medical conditions, the accurate knowledge of the local pressure inside a certain part of the body is very important, such as intracranial pressure or intravascular blood pressure monitoring. An acoustic sensor is a very interesting component for an implantable device, since it allows to capture ultrasound waves, hence it can be used as a sensor for acoustic waves for transmission of data, or as an energy scavenger collecting power from acoustic waves, allowing to charge a battery located inside the implanted electronic devices. Currently charging of implanted devices is performed using induction coils, but since electromagnetic fields are strongly absorbed by body tissue, induction based device powering is only possible for devices implanted close to the skin. Ultrasound waves are fully harmless for humans and their absorption by body tissue is low, hence a good acoustic sensor integrated in an implanted device would allow charging of this device even when it is implanted deep inside the body. 
test chip containing imec’s new MOMS-based pressure sensor
Fig. 3: test chip containing imec’s new MOMS-based pressure sensor, characterized by a superior precision in comparison with commercial MEMS, and which is able to monitor pressure over a very large pressure range. Such advanced sensors could be used in a variety of biomedical applications such as intracranial pressure or intravascular blood pressure monitoring, where high-quality remote sensing is required.
Having very interesting mechanical sensors developed at imec, and with a lot of experience in flexible packaging techniques for implants, we like to combine these two research domains in this PhD topic, in order to develop a suitable advanced packaging technology for various types of mechanical sensors. The package should be biocompatible and biostable for long term usage in the body, and it should be fully hermetic, hence preventing that any fluid penetrates into the package, as well as that solid device materials are diffusing through the package into the body. Furthermore, the encapsulation should be flexible, allowing an excellent functionality of the mechanical sensor which has moving, bending or flexing parts. The package might cause a change in sensor responsitivity, ie. by causing an offset in the sensor readout, but the readout should still be from high quality and the sensor should still be functional within the interesting measurement range. Finally, since implants for long term usage are envisaged, the encapsulation should allow many flexing/bending cycles of the mechanical sensor, without cracking nor losing its hermeticity, as well as without causing a gradual sensor readout shift nor increasing sensor noise over time. The PhD student will learn to characterize several of imec’s mechanical sensors which are interesting for implantable devices. The student will be trained to master the fabrication of such ultrathin flexible packages and will further adjust this package in order to obtain optimal results when applied for various types of mechanical sensors. Detailed characterization of the packaged sensors should be performed, with respect to sensor sensitivity, noise, stability over time, device hermeticity, etc. 
This research will be carried out on two locations: an important part of the work will be the encapsulation of the sensors, which will be performed at labs and in the cleanroom of CMST, imec’s associated lab at the University of Ghent, under supervision of the PhD promotor. Also hermeticity testing can be performed in the reliability labs of CMST in the city of Ghent. The modeling and characterization of the packaged sensors will be done at imec in the city of Leuven under supervision of the co-promotor, hence a strong collaboration with imec is envisaged. General research planning and follow-up during the PhD project will be in consultation with both involved research teams at CMST and at imec.
For more information about CMST/imec’s FITEP platform, please read: Maaike Op de Beeck et al., “Ultra-thin biocompatible implantable chip for bidirectional communication with peripheral nerves”, IEEE BIOCAS Conf., Oct. 2017, Torino, Italy; DOI: 10.1109/BIOCAS.2017.8325206



Required background: Engineering technology, Engineering science, Physics, or equivalent


Type of work: 50% experimental (cleanroom, lab), 10% modelling, 30% characterization and interpretation, 10% theory and literature study

Supervisor: Maaike Op de Beeck, Xavier Rottenberg

Daily advisor: Xavier Rottenberg, Maarten Cauwe

The reference code for this position is 1812-62. Mention this reference code on your application form.


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