Abstract
Abstract Application-specific integrated circuits (ASICs) embedded in polymers have been subject in implant manufacturing for the recent years. The increased functionality combined with good biocompatibility due to flexibility of thin implants makes them interesting for further studies. Thin-film ASICs can be used for the recording and processing of a high amount of biological signals, improving the performance of neural implants. Fabrication and analysis of gold and platinum thin-film connections are subject of this study, especially their capability as high frequency data transmission lines. Three layers of polyimide are used as flexible substrate and insulator of the traces. Various test structures were designed and fabricated, to investigate the resistance and reactance up to GHz frequencies, crosstalk and influence of vias between metallization layers. All conducting structures have a comparable design with a length of 50 mm and a metal thickness of 300 nm, while the line widths were varied. In this configuration gold and platinum thinfilm conductors are both suitable for high-frequency data transmission up to 100 MHz. This transmission frequency limit and impedances are unaffected by a wet environment and in accelerated aging tests. However, both metals show a high pass filter behavior, whose frequency behavior is mostly dependent by the self-inductance and resistance. A simplified ideal transmission model predicts the electrical behavior sufficiently and can be used to design the favored line impedance matching input impedances of the connected ASICs.
Highlights
The improvement of neural interfaces for electrical stimulation of nerves, has become increasingly important to help patients overcome physical impairments 1.For this purpose, a large number of implants with increasing complexity has been developed, i.e. high density electrode arrays 2
More advanced features could be realized with encapsulated Application-specific integrated circuits (ASICs), which have to be connected to the electrodes or terminals via a rising number of feedthroughs
Requirements for the encapsulations of ASICs are materials with a good adhesion, stability against water and vibration, a high breakdown voltage and no pin-holes after casting 3; all these requirements are met by polyimide (PI) 4
Summary
The improvement of neural interfaces for electrical stimulation of nerves, has become increasingly important to help patients overcome physical impairments 1. For this purpose, a large number of implants with increasing complexity has been developed, i.e. high density electrode arrays 2. An increasing number of interconnects between components, which are power transmission lines, and transmission links for highfrequency data communication could be realized 6. These thinfilm traces have to transmit even smallest electrical signals, with minor electrical losses and no, or at least low, crosstalk
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