Revitalizing polymer packaging for single-chip implants

Abstract

For over five decades, electronic implants have significantly improved the quality of life for millions of patients. With their great potential, substantial advancements have been made in developing new therapeutic devices, particularly in the fields of bioelectronic medicine and brain-machine interfaces. However, these emerging devices require novel approaches to packaging, as traditional hermetic enclosures no longer meet the physical and dimensional demands of modern systems. Polymer packaging offers a promising alternative, enabling device miniaturization and facilitating minimally invasive procedures. Polymer packaging was in fact one of the earliest methods used to protect electronics (implemented with discrete components) in the body. However, due to the inability of polymers to fully block moisture ingress, it soon became evident that the body’s wet and corrosive environment could negatively impact device longevity. As electronic implants evolved from using discrete components to complex integrated circuits (ICs), the challenge of protecting these devices became even more critical. In this thesis, I aimed to tackle the challenge of ensuring the safe and reliable operation of polymerpackaged ICs for long-term implantable applications. To address this challenge, I pursued three key objectives: 1) I developed on-chip sensor platforms to carefully monitor the integrity of the IC structure. These tools provide critical data on the condition and performance of the chips, ensuring their expected functionality in clinical settings. 2) I investigated the electrical and material stability of IC structures by directly exposing them as bare die (uncoated) to physiological environments, assessing their durability in the body’s corrosive conditions. By identifying potential degradation pathways, I proposed IC design guidelines that can potentially enhance the longevity of polymerpackaged devices. 3) I investigated if silicone rubber, as a polymer packaging material, could prevent or slow down the degradations seen in uncoated ICs. Separately, I also evaluated two thin-filmpackaging layers for their effectiveness in IC protection. Results demonstrated that IC structures can be inherently hermetic, enabling polymers, such as silicone, to serve as standalone packaging materials despite their moisture permeability. Furthermore, silicone was found to effectively prevent the degradations observed in bare-die ICs. Using advanced material analysis techniques, I derived degradation rates, showing that silicone-encapsulated ICs could last over 10 years in the body. These findings enable the development of long-lasting miniature implants, reducing the need for repeated surgeries and improving patients’ quality of life.