Dongyang Kang

High yield packaging for high-density multi-channel chip integration on flexible parylene substrate

This paper reports a new chip packaging technique for the assembly of retinal prosthesis device. Here, a photoresist is used as glue to attach a chip to the targeted parylene-C substrate so that 94% of the chip area is used as attachment to prevent delamination. As a validation, chips with 268 connections were used to assess the connection yield. The results show that this new technique, combined with an additional parylene-C coating, provide a high connection yield (>;90%) and is a promising method for high-lead-count implant devices.

Packaging study for a 512-channel intraocular epiretinal implant

Much effort has been put into developing multi-channel retinal prosthetic devices. Currently, even the most advanced prostheses do not have enough channels to provide vision to a desirable level. In this paper, we present a system design and a packaging scheme for a 512-channel intraocular epiretinal implant. Both a wireless power coil (with high transfer efficiency) and a data coil are included for this intraocular system. Simulation of the interference between coils is investigated and the results show that the two coils can be put in a co-planar fashion using two notch filters to minimize interference. The complete package is demonstrated with a mechanical model with a parylene-C flexible circuit board, i.e., parylene flex, to show the placement of the IC chips, discrete components, and coils. It also shows the final folded device after surgical insertion into an eye to save space. The feasibility of the proposed structure has been successfully tested in vivo. Experimentally, the maximum allowable pulling force is measured by a dynamic mechanical analysis (DMA) machine to be 8N, which provides a large safety margin for surgery.

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.

Study of the hybrid parylene/PDMS material

This paper reports the mechanical behavior and barrier property of the hybrid parylene/PDMS material. The repetitive uniaxial tensile tests are done to characterize its mechanical behavior and the water vapor transmission rate is measured to evaluate its barrier property. The experimental data are in accordance with the composite material theory. A novel approach of facilitating the diffusion and penetration of parylene coatings into PDMS using in-situ heated deposition is presented. The parylene depth profiling in PDMS and 180° peel tests demonstrate that parylene deposition at elevated temperatures shows enhanced pore sealing capability. A theoretical model is proposed, featuring an infinitely long cylindrical PDMS pore model, free molecular flow and time-varying pore geometry during the deposition. There is only one unknown parameter in the model: the PDMS pore diameter. By fitting the numerical solutions of the theoretical model to the parylene depth profiling curves, the PDMS pore diameter is estimated to be ~6.02nm.

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.

Isolation of circulating tumor cells by a magnesium-embedded filter

Circulating tumor cells (CTCs) are rare cancer cells that are shed by tumors into the bloodstream and that can be valuable biomarkers for various types of cancers. However, CTCs captured on the filter could not be released easily using the existing CTC analysis platforms based on size. To address this limitation, we have developed a novel magnesium (Mg)-embedded cell filter for capture, release and isolation of CTCs. The CTC-filter consists of a thin Ebeam-deposited Mg layer embedded between two parylene-C (PA-C) layers with designed slots for filtration and CTC capture. Thin Mg film has proved highly biocompatible and can be etched in saline, PBS and Dulbeccos modified eagle medium (DMEM) etc, properties that are of great benefit to help dissociate the filter and thus release the cells. The finite element method (FEM) analysis was performed on the Mg etching process in DMEM for the structure design. After the filtration process, the filter was submerged in DMEM to facilitate Mg etching. The top PA-C filter pieces break apart from the bottom after Mg completely dissolves, enabling captured CTCs to detach. The released CTC can be easily aspirated into a micropipette for further analysis. Thus, the Mg-embedded cell filter provides a new and effective approach for CTCs isolation from the filter, making this a promising new strategy for cancer detection.

Reliable deposition of ultra-thin parylene

This paper reports a novel and reliable process to prepare ultra-thin parylene film based on a principle combining both molecular effusion and diffusion. For the first time, a technique for the deposition of parylene film thinner than 20 nm in a highly controllable and repeatable way is developed. Parylene films with various thicknesses could also be prepared in a single deposition run by using this method. This technique holds promising potentials in extensive applications, such as protection/dielectric layer for needle electrodes and flexible electronics, semi-permeable membrane, and other polymer engineering.

Magnesium-embedded live cell filter for CTC isolation

This paper reports a novel Magnesium-embedded cell filter for Circulating Tumor Cell (CTC) capture, release and isolation. The new and novel feature is the use of thin-film Mg to release the captured CTCs based on the fact that any Cl- containing culture medium can readily etch Mg away [1]. The releasing and the isolation of each individual CTC are demonstrated here. After filtration process, the filter is submerged in PBS to facilitate Mg etching. The top PA-C filter pieces break apart from the bottom after Mg completely dissolves, enabling captured CTC cells to detach from the filter. The released CTC can then be easily aspirated into a micropipette, and then for further, such as, DNA mutation analysis.

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.