Abstract
A new class of wireless neural interfaces is under development in the form of tens to hundreds of mm-sized untethered implants, distributed across the target brain region(s). Unlike traditional interfaces that are tethered to a centralized control unit and suffer from micromotions that may damage the surrounding neural tissue, the new free-floating wireless implantable neural recording (FF-WINeR) probes will be stand-alone, directly communicating with an external interrogator. Towards development of the FF-WINeR, in this paper we describe the micromachining, microassembly, and hermetic packaging of 1-mm3 passive probes, each of which consists of a thinned micromachined silicon die with a centered Ø(diameter) 130 μm through-hole, an Ø81 μm sharpened tungsten electrode, a 7-turn gold wire-wound coil wrapped around the die, two 0201 surface mount capacitors on the die, and parylene-C/Polydimethylsiloxane (PDMS) coating. The fabricated passive probe is tested under a 3-coil inductive link to evaluate power transfer efficiency (PTE) and power delivered to a load (PDL) for feasibility assessment. The minimum PTE/PDL at 137 MHz were 0.76%/240 μW and 0.6%/191 μW in the air and lamb head medium, respectively, with coil separation of 2.8 cm and 9 kΩ receiver (Rx) loading. Six hermetically sealed probes went through wireless hermeticity testing, using a 2-coil inductive link under accelerated lifetime testing condition of 85 °C, 1 atm, and 100%RH. The mean-time-to-failure (MTTF) of the probes at 37 °C is extrapolated to be 28.7 years, which is over their lifetime.
Highlights
As neural interfaces strive to more effectively interact with the brain, neural recording and modulation of the future will need the ability to simultaneously interface with multiple sites distributed across large areas of the brain [1,2]
To address the aforementioned problems, we introduce the concept of a distributed free-floating wireless implantable neural recording (FF-WINeR) system, which is powered via EM in near-field, using magnetic resonance
In the current proof-of-concept prototype, each FF-WINeR probe includes one to four sharpened penetrating Tungsten microwire electrodes for neural recording, a soft-wire non-penetrating reference electrode, a thinned micromachined silicon die that serves both as the probe substrate for mechanical support and houses the application-specific integrated circuit (ASIC), two surface mount device (SMD) capacitors mounted on the silicon die, a bonding-wire coil wound around the die, and hermetic packaging including parylene-C and polydimethylsiloxane (PDMS) coatings
Summary
As neural interfaces strive to more effectively interact with the brain, neural recording and modulation of the future will need the ability to simultaneously interface with multiple sites distributed across large areas of the brain [1,2]. In the current proof-of-concept prototype, each FF-WINeR probe includes one to four sharpened penetrating Tungsten microwire electrodes for neural recording, a soft-wire non-penetrating reference electrode, a thinned micromachined silicon die that serves both as the probe substrate for mechanical support and houses the application-specific integrated circuit (ASIC), two surface mount device (SMD) capacitors mounted on the silicon die, a bonding-wire coil wound around the die, and hermetic packaging including parylene-C and polydimethylsiloxane (PDMS) coatings.
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