Feasibility of LCP as an Encapsulating Material for Photodiode-Based Retinal Implants

While retinal implants based on microphotodiode array (MPDA) could achieve great number of channels without an external camera, the absence of proper packaging technology of MPDA has limited their use in chronic implantation. Liquid crystal polymer (LCP) has gained increasing attention as a biomaterial for implantable devices due to its low water absorption rate and low permeability. In this letter, feasibility of LCP film as an encapsulation material of photodiode-based retinal prosthesis was explored. Optical property of LCP was measured to find the film thickness that can guarantee the light transmittance greater than 20%, which was achieved by developing the dry etching process of commercial LCP films to be less than 10
$\mu \text{m}$
. The minimum distinguishable line pitch of the thin LCP encapsulation evaluated by a custom setup with projected grating patterns on CMOS image sensor was 90
$\mu \text{m}$
, which could be equivalent to ideally 1200 channels in macular area of 10 mm
²
.