Integrated wireless neural interface based on the Utah electrode array

Abstract

This report presents results from research towards a fully integrated, wireless neural interface consisting of a 100-channel microelectrode array, a custom-designed signal processing and telemetry IC, an inductive power receiving coil, and SMD capacitors. An integration concept for such a device was developed, and the materials and methods used to implement this concept were investigated. We developed a multi-level hybrid assembly process that used the Utah Electrode Array (UEA) as a circuit board. The signal processing IC was flip-chip bonded to the UEA using Au/Sn reflow soldering, and included amplifiers for up to 100 channels, signal processing units, an RF transmitter, and a power receiving and clock recovery module. An under bump metallization (UBM) using potentially biocompatible materials was developed and optimized, which consisted of a sputter deposited Ti/Pt/Au thin film stack with layer thicknesses of 50/150/150 nm, respectively. After flip-chip bonding, an underfiller was applied between the IC and the UEA to improve mechanical stability and prevent fluid ingress in in vivo conditions. A planar power receiving coil fabricated by patterning electroplated gold films on polyimide substrates was connected to the IC by using a custom metallized ceramic spacer and SnCu reflow soldering. The SnCu soldering was also used to assemble SMD capacitors on the UEA. The mechanical properties and stability of the optimized interconnections between the UEA and the IC and SMD components were measured. Measurements included the tape tests to evaluate UBM adhesion, shear testing between the Au/Sn solder bumps and the substrate, and accelerated lifetime testing of the long-term stability for the underfiller material coated with a a-SiC(x):H by PECVD, which was intended as a device encapsulation layer. The materials and processes used to generate the integrated neural interface device were found to yield a robust and reliable integrated package.

Recent advances in flexible sensors for wearable and implantable devices

“…10,11,25 It seems that conventional devices based on microelectrode arrays have potential limitations, including insufficient spatial density and the possibility of damaging adjacent soft tissue with their intrinsic rigidity. [80][81][82][83][84] Hence, a minimally invasive and nonpenetrating measurement system is required for in vivo diagnostic and therapeutic devices with the capability of having large-area coverage and providing high performance and sufficient spatial resolution.…”

Optical microlithography on oblique and multiplane surfaces using diffractive phase masks

“…10 In addition, micropatterning on the sidewalls of implantable neural probes could potentially lead to an effective approach of recording threedimensional (3-D) neural signals. 11,12 Meanwhile, shape modification in the vertical direction of microfluidic channels and 3-D integration may significantly enhance their performances. 5,13 Optical projection lithography (OPL) on planar silicon substrates is the workhorse of the semiconductor industry due to its high throughput, resolution, and accuracy.…”

Flexible and stretchable micro-electrodes for in vitro and in vivo neural interfaces

“…Penetrating MEAs are based on needle-like structures, which are pushed into the brain or the nerve in vivo [15,19]. They are fabricated with silicon or titanium.…”

“…They are fabricated with silicon or titanium. They may comprise a single needle bearing multiple contacts on its shaft [20,39] or a 10 9 10 matrix of single contact electrodes [19,36]. Successful penetrating electrodes are already available to humans, e.g., cochlear implants [40] and deep brain stimulator [10,17].…”