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Diamond at the brain-machine interface

Edgington, R.; (2012) Diamond at the brain-machine interface. Doctoral thesis, UCL (University College London). Green open access

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Abstract

Electrodes at the Brain Machine Interface (BMI) must fulfil tall specifications: They must have excellent electrical properties to transduce electrogenic activity, be highly biocompatible and not degrade in a saline environment over the lifetime of the patient. In this respect, diamond is an excellent BMI material. In this thesis, the application of diamond at the BMI is investigated. Results Chapter 5 discusses the use of nanodiamond (ND) monolayers to promote the formation of functional neuronal networks. Neurons cultured on ND-coated substrates perform remarkably well, and similar to those grown on standard protein-coated materials with respect to their initial cell attachment, outgrowth, neuronal excitability and functionality of the resulting networks. NDs bypass the necessity of protein coating and show great potential for chronic medical implants. Chapter 6 describes the fabrication of nanocrystalline diamond (NCD) Micro-Electrode Arrays (MEAs) for the recording of electrogenic cells. MEAs are fabricated with metallic boron-doped nanocrystalline diamond (BNCD) and passivated with NCD, SiO2/Si3N4/SiO2 stacks and SU-8 epoxy. The recording of electrogenic activity of HL-1 cardiac cells is demonstrated with high signal-to-noise ratios and low signal loss. Chapter 7 and Chapter 8 describe the development of boron-doped (111) diamond Solution Gate Field-Effect Transistors (SGFETs). In Chapter 7 an optimised Plasma Enhanced Chemical Vapour Deposition (PECVD)-doping recipe using the (111) diamond plane is presented. AC Hall characterisation yields desirable sheet carrier densities for FET application with enhanced carrier mobilities, and Impedance Spectroscopy (IS) measurements divulge metallic electrical properties with low activation energies, indicative of heavily doped diamond as confirmed by Secondary Ion Mass Spectroscopy (SIMS). Chapter 8 describes the fabrication of boron δ-doped (111) diamond SGFETs (δ-SGFETs). δ-SGFETs show improved I-V characteristics in comparison to previous similar devices, whereby the enhancement mode operation, channel pinch-off and current saturation are achieved within the electrochemical window of diamond. Considering the biocompatibility of diamond towards cells, δ-SGFETs are promising for recording electrogenic cells.

Type:Thesis (Doctoral)
Title:Diamond at the brain-machine interface
Open access status:An open access version is available from UCL Discovery
Language:English
UCL classification:UCL > School of BEAMS > Faculty of Engineering Science > Electronic and Electrical Engineering

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