Jay Han-Chieh Chang

Adhesion-enhancing surface treatments for parylene deposition

Parylene-C has been extensively used in biomedical devices as a conformal and biocompatible coating. It is also a good material for implantation. Unfortunately, serious delamination between parylene-C and other materials is often found even during standard MEMS processes such as lift-off and sacrificial photoresist releasing. Therefore, surface treatments before parylene deposition that can enhance the interface adhesion between the deposited parylene and the coated surface are highly desirable. Interestingly, the chemical structure of Parylene-C does suggest that parylene-C deposition on a clean hydrophobic surface favors a good interface adhesion. This work is then to study various surface treatments, especially on silicon and another parylene-C surfaces, by hexane, toluene, propylene carbonate (P.C.), and tetrafluoromethane (CF4) plasma. Our hypothesis is then good surface cleaning can lead to interface adhesion. We report the results here using parameters such as peeling force, soaking undercut rate, and vertical attack bubble density (VABD) to quantify the effectiveness of these adhesion treatments.

High density 256-channel chip integration with flexible parylene pocket

Current state-of-the-art technologies for retinal prosthetics suffer greatly from complicated IC packaging with high lead count because there is the lack of high density and high lead-count connection. To overcome this challenge, we develop here a packaging technique that utilizes a flexible parylene pocket with metal pads to house a chip for aligned connection. This reported pocket can be designed with the right size to house any IC chip and/or a discrete component. As a demonstration, a 256-channel conduction chip along with an RFID chip have been connected and tested with this technique. The results show that this new technique can be further improved to achieve 10,000 connections within an area of 1 cm2.

High-density IC chip integration with parylene pocket

We utilize the parylene pocket technology and develop a novel integration scheme that will allow us to connect more than 100 bonding pads on an area less than 5 mm × 5 mm with high efficiency. This packaging technique can also house any IC chip or discrete component and provide electrical connection to it. Here we use squeegee technique to connect each pad on the chip with the bonding pad on the pocket to achieve functionality because the chip that is to be integrated in this section has a very dense array and it is impractical and extremely difficult to connect everything manually. Devices testing are done by testing dummy chip integration and soaking test. Positive results prove that such parylene pocket packaging technique works well.

MEMS oxygen transporter to treat retinal ischemia

For the first time, a paradigm shift in the treatment of retinal ischemia is proposed: providing localized supplemental oxygen to the ischemic tissue via an implanted MEMS device. A passive MEMS oxygen transporter is designed, built and tested in both artificial eye models and porcine cadaver eyes to confirm various hypotheses. The finite element modeling results predict that the proposed approach can treat complete retinal ischemia.

Effects of deposition temperature on Parylene-C properties

This paper reports the study of in-situ deposition temperature (ranging from 20°C to 80°C) effects on Parylene-C properties in terms of glass transition temperature (Tg), β-relaxation temperature (Tβ), Youngs modulus and crystallinity (including crystallite size). The results show that the Parylene-C (PA-C) thin film deposited at higher deposition temperature exhibits higher Tg and Tβ, revealing that the movement of the molecular backbones is further frozen and restricted. It is physically consistent with the data showing that higher deposition temperature induces greater degree of crystallinity and larger Youngs modulus. With the new knowledge, Parylene-C thin film with properties tailored to various requirements could be achieved by choosing the proper deposition temperature.

Long term glass-encapsulated packaging for implant electronics

Hermetic Titanium-alloy packaging (e.g., used in pacemakers and cochlear implants) has been accepted as the industrial standard for decades. However, two remaining issues of this well-known technology are the size and limited number of feedthroughs [1]. On the other hand, the next generation wireless intraocular retinal prosthetic devices do require unprecedented small size and large number of leads to be fitted inside a human eyeball so the traditional metal packaging is difficult to be implemented. Therefore, these new generation of microimplants will need a new packaging scheme. This paper then reports a new long-term packaging method using glass encapsulation featuring a controlled failure mode from fast diffusion to slow undercut. The results is promising that this new packaging scheme could survive more than 10 years by accelerated “active” lifetime soaking test (i.e., with electric field applied) in 0.9 wt.% saline solution. As a whole, this new method provides several advantages including easy employment, controllable long life time, and enhanced heat dissipation.

In situ heating to improve adhesion for parylene-on-parylene deposition

A new technique of using “in-situ heating” to enhance adhesion for parylene-on-parylene deposition is reported in this paper. This method is compared with existing physical or chemical adhesion-enhancing methods and the results show clear advantages of this new technique. The physics is believed to be that the mobility of deposition-involved molecules (including the substrate parylene polymer chains and adsorbed monomers during deposition) is enhanced when deposition temperature rises, especially above the glass transition temperature of the substrate parylene. Each sample is patterned and then soaked in 0.9% saline at 90°C, and the undercut between two parylene layers due to the attack from saline during the soaking test could be observed. The undercut rate is measured to quantify the adhesion strength.

Thin-film magnesium as a sacrificial and biodegradable material

This work reports the study of ebeam-deposited thin-film magnesium (Mg) as a sacrificial and a biodegradable material. We have tested etchants including diluted hydrochloric acid (HCl), saline, and culture medium. Both vertical etching method and channel undercut method are used to characterize the Mg etching properties. The initial results confirm that thin-film Mg is a promising dual sacrificial and biodegradable material. In addition, an etching model, which fits accurately the etching length vs. time over a wide range of HCl concentrations (0.02-1M) is developed. This model is based on diffusion and a combined first-and-second order chemical reaction mechanism.

Dry mechanical liftoff technology for metallization on parylene-C using SU-8

This paper presents a new fabrication method to employ dry mechanical liftoff of SU-8 mask to pattern metals on parylene-C film. Soaking tests were done to examine the adhesion between SU-8 and parylene-C film with different interface treatments. SU-8 masks with different thickness were tested in order to find out the best trade-off between the feature sizes and the easiness of removal from paryelene-C film after metal deposition. Features from 10 μm to 300 μm in diameter and width were successfully patterned on parylene-C film by this method. The 15 μm thick SU-8 liftoff mask is highly flexible and can be peeled off mechanically from parylene-C film by tweezers seconds without any visible residue. Metal lines with testing pads from 10 μm to 100 μm wide and 1 cm long were also fabricated and tested to evaluate their resistances. this new method provides an alternative way of metallization on parylene-C film which benefits the application in MEMS area.

Time-dependent cell membrane damage under mechanical tension: Experiments and modeling

This paper reports a study of cancer cell membrane damage during filtration caused by cell membrane tension. The membrane tension was induced when cells were captured on a microfabricated parylene-C filter during the constant-pressure-driven filtration. This work includes both experiments and modeling to explore the underlying biomechanics of the cell membrane damage. The developed model not only agrees with our time-dependent cell damage data, but also fits well with previous results on red blood cells reported by other groups.