Fabrication and validation of flexible neural electrodes based on polyimide tape and gold sheet.

This research was conducted to apply polyimide tape, which has the advantages of low price ans strong adhesive strength, to the neural electrode process. In addition, to maximize the low-cost characteristics, a fabrication process based on UV laser patterning rather than a photolithography process was introduced. The fabrication process started by attaching the gold sheet on the conductive double-sided tape without being torn or crushed. Then, the gold sheet and the double-sided tape were patterned together using UV laser. The patterned layer was transferred to the single-side polyimide tape. For insulation layer, electrode site opened single-sided polyimide tape was prepared. Polydimethylsiloxane was used as an adhesion layer, and alignment between electrode sites and opening sites was processed manually. The minimum line width achieved through the proposed fabrication process was approximately 100 µm, and the sheet resistance of the conductive layer was 0.635 Ω/sq. Measured cathodal charge storage capacity was 0.72 mC/cm2 and impedance at 1 kHz was 4.07 kΩ/cm2. Validation of fabricated electrode was confirmed by conducting 30 days accelerated soak test, flexibility test, adhesion test and ex vivo stimulation test. The novel flexible neural electrodes based on single-sided polyimide tape and UV laser patterned gold sheet was fabricated successfully. Conventional neural electrode fabrication processes based on polyimide substrate has a disadvantages such as long fabrication time, expensive costs, and probability of delamination between layers. However, the novel fabrication process which we introduced can overcome many shortcomings of existing processes, and offers great advantages such as simplicity of fabrication, inexpensiveness, flexibility and long-term reliability.

Investigation of toxicity and performance deterioration of parylene-C packaged copper coils using accelerated test.

OBJECTIVES: In this paper, to figure out the reliability of copper wire wound coil in an in vitro environment, performance deterioration and copper ion elution of coil was investigated using accelerated tests. METHODS: Bare coils with enamel coating and parylene-C coated coils were immersed into the 75-degree Celsius phosphate-buffered saline for accelerated tests. Performance and elution of the copper ion were investigated using proper equipment. RESULTS: The parylene-C coating with a thickness of several um effectively depress the performance degradation and the elution of the copper ion. However, it has not reached a perfect level and research on additional packaging methods is needed. SIGNIFICANCE: Coil for wireless power and data transfer is an important element in the design of implantable devices. Copper is the most widely used material for the design of coils in general. However, because of its cytotoxicity and high reactivity with water, the packaging capabilities should be investigated closely. In this paper, a method for evaluating the packaging performance when the coil is coated with parylene-C and the results are presented.

Fabrication of Implantable Microelectrode Array using Cyclic Olefin Copolymer and SU-8 via Photocrosslinking Lamination.

In this work, a fabrication process for implantable electrodes using a Cyclic Olefin Copolymer (COC) substrate and a SU-8 passivation layer was presented. COC and SU-8 were shown to be suitable for implantable neural electrodes due to their biocompatibility, chemical resistance, and thermal stability. The electrodes were successfully patterned on the COC film, and the SU-8 passivation layer was coated while maintaining site-opened via photolithography. The photocrosslinking lamination of the substrate and passivation layer was used to produce electrodes with fine line widths of 20um without applying heat.

Low dead space encapsulation and integration of circuits for retinal prosthesis based on cyclic olefin copolymer.

A retinal prosthesis is a device that can provide artificial vision to people who have lost their sight from certain retinal disorder. Because the device needs to be inserted into the body, high flexibility and reliability is required. Recently, devices using thermoplastic polymers such as LCP and COC as substrates have been studied. Being a highly functional integrated device, retinal prosthesis poses many design challenges. Among them, the stimulation chip embedding can be a particularly important task. Although it is common to use a wire bonding method for chip embedding, there are several limitations that are difficult to apply to implantable device. In this investigation, a novel approach is developed for high spaceefficient electrical connections and perform reliable encapsulation of integrated circuits to replace wire bonding. Since designing and manufacturing the stimulator chip used in retinal prosthesis requires non-negligible cost, a silicon die with the identical shape was selected as a substitute for testing purposes.

Neurostimulators for high-resolution artificial retina: ASIC design challenges and solutions.

Objective.Neurostimulator is one of the most important part in artificial retina design. In this paper, we discuss the main challenges in the design of application-specific integrated circuit for high-resolution artificial retina and suggest corresponding solutions.Approach. Problems in the design of the neurostimulator for the existing artificial retina have not been solved yet are analyzed and solutions are presented. For verification of the solutions, mathematical proof, MATLAB and Ansys simulations are used.Main results. The drawbacks of resorting to a high-voltage complementary metal oxide semiconductor (CMOS) process to deal with the large voltage compliance demanded by the stimulator output stage are pointed out, and an alternative approach based on a circuit that switches the voltage of the common reference electrode is proposed to overcome. The necessity of an active discharge circuit to remove the residual charge of electrodes caused by an unbalanced stimulus is investigated. We present a circuit analysis showing that the use of a passive discharge circuit is sufficient to suppress problematic direct current in most situations. Finally, possible restrictions on input and output (I/O) count are investigated by estimating the resistive-capacitive delay caused by the interconnection between the I/O pad and the microelectrode array.Significance. The results of this paper clarified the problems currently faced by neurostimulator design for the artificial retina. Through the solutions presented in this study, circuits with more competitiveness in power and area consumption can be designed.

Investigation of neural electrode fabrication process on Polycarbonate substrate.

Polycarbonate is a polymer that has been widely used including medical application due to its useful properties. It has high temperature resistance, biocompatibility, transparency and low water absorption rate, which are needful characteristics for packaging material of implantable neural prosthetic devices. In this study, we investigated fabrication of neural electrode with polycarbonate film using standard photolithography process and heated hydraulic press for thermal lamination. First, oxygen plasma surface treatment was performed to increase the adhesion between metal and polycarbonate film. Then thin layer of titanium and gold layer were deposited. Metal layer is patterned through standard photolithography techniques. After completing the metal patterning, thermal lamination was performed with site opened polycarbonate film.

Electrode design on plastic substrates using laser patterned double-sided tape and gold leaf.

The production of electrodes and sensors using plastic substrates has increased substantially for the last decades. Although devices are fabricated using plastic substrates suitable for the purpose of each device, it is difficult to find a process that can be used commonly for most types of plastics. In this paper, two kinds of electrode fabrication process that can be applied to most plastic films using kapton double sided tape and gold leaf are proposed. One is for the plastic film with adhesive and the other is for the film without adhesive. First, the kapton double-sided tape was patterned using a CO2 laser. After transfer double-sided tape to desired substrate, release paper was detached and gold leaf was attached on the exposed side of the tape. Then, the tape was appropriately removed according to the presence or absence of the adhesive. After that, the packaging was performed using an adhesive when the used film has adhesive, and otherwise, heat press was used for packaging. These processes have a variety of advantages such as inexpensive, fast-running and commonly applicable to many plastics. To prove its usability, impedance and minimum line width was measured.