Conductive graphitic wires generation in diamond by means of pulsed Bessel beam micromachining

At a Glance

Metadata	Details
Publication Date	2023-01-01
Journal	EPJ Web of Conferences
Authors	Akhil Kuriakose, Andrea Chiappini, Belén Sotillo, Adam Britel, Pietro Aprà
Institutions	Universidad Complutense de Madrid, University of Turin
Analysis	Full AI Review Included

Conductive Graphitic Wires in Diamond: Technical Analysis

This analysis focuses on the fabrication of transverse graphitic microelectrodes in synthetic diamond using pulsed Bessel beam micromachining, optimized for high conductivity and integration into diamond-based devices.

Executive Summary

Core Achievement: Successful fabrication of high-quality, transverse graphitic microelectrodes spanning the entire 500 µm thickness of monocrystalline CVD diamond samples.
Methodology: Utilized non-diffracting Bessel beams (BB) generated by an axicon, allowing for single-pass, multiple-shot writing without the need for sample translation along the beam propagation axis.
Performance Metric: Achieved a record-low resistivity of 0.04 Ω cm for Bessel beam-written graphitic structures in diamond, demonstrating high conductivity suitable for device integration.
Optimal Parameters: Best conductivity was obtained using a longer pulse duration (10 ps) combined with 6 µJ pulse energy, which Micro-Raman confirmed resulted in superior diamond-to-graphite phase transformation compared to femtosecond pulses (200 fs).
Beam Specifications: The Bessel beam featured a 3 µm core size and a 700 µm non-diffracting length, ensuring the focal region crossed the entire sample thickness.
Application Relevance: These integrated conductive structures are crucial for creating internal electric field sources and current collection pathways in advanced diamond detectors and integrated circuits.

Technical Specifications

Parameter	Value	Unit	Context
Sample Material	Monocrystalline CVD Diamond	N/A	(100) and (110) orientations tested
Sample Thickness	500	µm	Transverse electrode length
Laser System	Ti:Sapphire Amplified	N/A	20 Hz repetition rate
Laser Wavelength	790	nm	Fundamental wavelength
Baseline Pulse Duration	40	fs	Transform-limited pulse
Machining Pulse Duration Range	200 fs to 10	ps	Tunable regime
Optimal Pulse Duration	10	ps	Yielded best conductivity
Optimal Pulse Energy	6	µJ	Used for lowest resistivity measurement
Bessel Beam Core Size	3	µm	Transverse dimension
Non-Diffracting Length	700	µm	Focal region length (greater than sample thickness)
Achieved Resistivity (Lowest)	0.04	Ω cm	Measured via 2-probe IV configuration
Shots per Electrode (Example)	9000	Pulses	Example for 200 fs, 5 µJ fabrication
Raman Spectral Resolution	~1	cm^-1	Used for crystallinity analysis

Key Methodologies

Laser Source and Shaping: A 20-Hz Ti:Sapphire amplified laser system (790 nm) was used. The Gaussian output beam was reshaped into a finite energy Bessel beam (BB) using a conical lens (axicon).
Beam Delivery and Alignment: A telescopic system demagnified the BB to achieve a 3 µm core size and a 700 µm non-diffracting length. The beam was aligned orthogonally to the sample surface such that the BB focal length crossed the entire 500 µm sample thickness.
Micromachining Process: Fabrication was performed in a multiple-shot regime (e.g., 9000 pulses) by injecting the laser pulses orthogonally to the surface. Crucially, no sample translation was required along the beam propagation direction.
Parameter Optimization: The process was optimized by varying pulse duration (200 fs up to 10 ps) and pulse energy (mJ range) on both (100) and (110) oriented diamond samples.
Crystallinity Analysis: Micro-Raman spectroscopy was performed on the top surface of the wires to evaluate the degree of diamond-to-graphite phase transformation, confirming that 10 ps pulses provided superior conversion.
Electrical Characterization: Current-voltage (IV) measurements were conducted using a 2-probe configuration in an IVT chamber to determine the resistivity of the fabricated microelectrodes.

Commercial Applications

The ability to embed highly conductive, 3D graphitic structures within bulk diamond enables several high-performance engineering applications:

High Energy Particle Detectors: Integration of internal electrodes for efficient charge collection and precise electric field shaping, leveraging diamond’s radiation hardness and wide bandgap.
Integrated Photonic Circuits: Creation of active components, such as integrated heaters or modulators, by incorporating conductive elements directly into diamond waveguides and chips.
Microfluidic and Bio-Sensing Systems: Utilizing the chemical inertness and biocompatibility of diamond, the embedded electrodes can be used for localized electrochemical sensing or electrokinetic fluid manipulation.
3D Electronic Packaging: Fabrication of high-density, vertical interconnects (vias) within diamond substrates, crucial for advanced 3D stacking and packaging of high-power electronic chips.
Thermal Management: Using the graphitic wires as localized resistive heating elements or temperature sensors within diamond substrates for precise thermal control in microelectronic devices.

View Original Abstract

We present the fabrication of transverse graphitic microelectrodes in a 500 μm thick synthetic diamond bulk by means of pulsed Bessel beams. By suitably placing the elongated focal length of the Bessel beam across the entire sample, the graphitic wires grow from the bottom surface up to the top during multiple shot irradiation. The morphology of the microstructures generated and the micro-Raman spectra are studied as a function of the laser parameters and the diamond crystal orientation. We show the possibility to generate high conductivity microelectrodes, which are crucial for the application of electric fields or current transport/collection in various chips and detectors.

Tech Support

Original Source

DOI: https://doi.org/10.1051/epjconf/202328705016