# Neural Probe

- Organization: [Biomedical Microsystems Laboratory, USC](https://biomems.usc.edu/)
- Role: Design, Fabrication, & Characterization
- Dates: Jul 2024 – May 2025
- Supervisor: Professor Ellis Meng
- Funding: [CURVE Fellowship](https://viterbiundergrad.usc.edu/research/curve/); [USC Provost's Undergraduate Research Fellowship](https://academicprograms.usc.edu/services/undergraduate-research-and-experiential-learning/usc-provosts-undergraduate-research-fellowships/)
- Topics: Neural interfaces, Microfabrication, COMSOL, PCB design, Fusion 360, KLayout, Parylene
- Page: https://www.cedarroseleach.com/work/neural-probe/

> Helped design, fabricate and characterize a flexible neural recording probe that pairs polymer flexibility with silicon electrode density, including two custom PCBs and COMSOL coil simulations.

Links:
- [Symposium poster (PDF)](https://www.cedarroseleach.com/files/neural-probe-poster.pdf)
- [Project description (PDF)](https://www.cedarroseleach.com/files/neural-probe-project-description.pdf)

Publications:
- Conference abstract: Barrera, N.D., Nguyen, T.D., Ramirez, E., Leach, C.R., Abbasi, N., Molisch, A., Sideris, C., & Meng, E. "Implantable Flexible GHz Waveguide for High Data Throughput Neural Recording Interfaces." Neural Interfaces 2025 Conference, June 2025.
- Poster: Leach, C.R., Barrera, N., Ramirez, E., & Meng, E. "Development and Characterization of a High-Density Flexible Neural Recording Probe." Research symposium poster, University of Southern California, 2025. https://www.cedarroseleach.com/files/neural-probe-poster.pdf

Since July 2024, I've been helping to design, fabricate, and characterize a hybrid silicon-polymer neural recording probe.

This neural probe aims to combine the flexibility of polymer-based neural interfaces and the high electrode density of silicon-based neural interfaces. This hybrid approach enforces high spatial resolution neural recordings while maintaining flexible mechanical properties and biocompatibility required for neural implants. To create this novel neural probe, I am assisting in developing and testing the fabrication procedure for the flexible shank.

I joined this lab last summer after a month of training in semiconductor fabrication processes in the cleanroom. I was able to translate this knowledge of nanofabrication to the lab's development of neural interfaces. I truly enjoy the process of creating this device. It's a ton of trial and error, brainstorming different fabrication methods and figuring out what works and what doesn't. I can think of at least six different fabrication approaches that we have undertaken, and each approach has many different variations - tweaking the mold CAD file, or the material of the coil, or the method of transferring the coil to the substrate, or the coil-forming strategies.

There are standard fabrication processes for creating neural probes (e.g. photolithography, deposition, etching, liftoff). However, our project requires a new fabrication approach since we are dealing with a much thicker layer of conductive material.

Throughout the process of brainstorming, designing, fabricating, and characterizing the neural probe, I have gained valuable knowledge and honed a variety of skills, including:

### Femtosecond Laser Ablation
To precisely pattern coils from a titanium sheet for one rendition of the neural probe.

### Fusion 360 CAD
Created the mold for forming a wire into the desired shape of the primary coil.
Developed multiple mold variations to optimize both the coil's geometry and the efficiency of the wire-forming process.

### K-Layout
Designed 2D coil patterns for fabrication on silicon wafers.

### Device Packaging
Soldering and coil molding to create the primary coil and neural probe shank. Attached SMA connectors for testing and measurements.

### S-param Data Analytics
S to Z conversion to analyze impedance of primary coil and derivation of inductance.

### COMSOL Simulations
Learned COMSOL, simulating magnetic field and inductance properties of the probe to optimize coil performance.

### Parylene Deposition & Etching
Worked in the cleanroom depositing parylene for various renditions of the probe. Parylene serves as an insulator and a substrate for the probe.

### Analog-to-Digital Converter (ADC)
Researched and selected ADC eval boards as to digitize probe data. Focused on specifications such as sampling rate & bit resolution.

### PCB Design
Designed two custom PCBs. The latest is a testing tool for evaluating inductive coupling efficiency of the neural probe's primary coil. I configured dual RF amplifiers to measure voltage differentials across the ports and calculated trace widths for impedance matching. The second board just adapts a ZIF connector to Molex pins, but I made it 10x cooler with cute seal saying hi.

Figures:
- Symposium poster
- PCB with secondary coil for testing inductive coupling efficiency of primary coil
- ZIF connector

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By Cedar Rose Leach (cdleach@usc.edu). Site summary: /llms.txt