Nanoladder Cantilevers Made from Diamond and Silicon

At a Glance

Metadata	Details
Publication Date	2018-02-07
Journal	Nano Letters
Authors	M Héritier, Alexander Eichler, Ying Pan, Urs Grob, Ivan Shorubalko
Institutions	Swiss Federal Laboratories for Materials Science and Technology, ETH Zurich
Citations	46
Analysis	Full AI Review Included

Technical Analysis & Product Solution Brief: MPCVD Single Crystal Diamond for Ultra-Sensitive Nanoladder Cantilevers

Executive Summary

This research establishes the nanoladder geometry as the state-of-the-art platform for ultrasensitive, top-down batch-fabricated nanomechanical cantilevers, leveraging the exceptional properties of Single Crystal Diamond (SCD).

Record Sensitivity: The nanoladder design achieves the lowest reported thermal force noise (F_th) for a cantilever device to date, reaching 0.19 aN/√Hz (at 100 mK) using diamond SCD.
Geometric Advantage: The design significantly reduces both effective mass (m) and spring constant (k) by approximately two orders of magnitude compared to standard rectangular beams of similar dimensions, resulting in a 15-fold reduction in mechanical dissipation (γ).
Material Performance: Electronic-grade SCD exhibited extraordinarily high mechanical quality factors (Q) up to 162,000 at millikelvin temperatures, proving diamond’s superior suitability for cryogenic quantum measurements.
Scalability: The top-down fabrication process, utilizing Electron Beam Lithography (EBL) and Inductively Coupled Plasma (ICP) etching, validates the scalability and geometric reproducibility required for commercial applications like Scanning Force Microscopy (SFM) and Magnetic Resonance Force Microscopy (MRFM).
Future Applications: The achieved sensitivity surpasses the required threshold for detecting the force generated by a single nuclear spin (estimated at 400 zN), paving the way for atomic-resolution magnetic imaging.

Technical Specifications

Performance characteristics for the primary Single Crystal Diamond (SCD) Nanoladder device analyzed in this work (Device #1, L=150 µm).

Parameter	Value	Unit	Context
Material	Single Crystal Diamond (SCD)	N/A	Electronic grade, (100) orientation
Cantilever Length (L)	150	µm	Typical investigated length (100-300 µm range)
SCD Thickness (T)	20	µm	Polished layer thickness
Feature Size (Rails/Rungs)	100 - 300	nm	Minimum lateral dimensions
Resonance Frequency (f_c)	25.22	kHz	Fundamental mechanical mode
Effective Mass (m)	4.1 ± 0.6	pg	Ultra-low mass achieved by geometry
Spring Constant (k)	110 ± 10	µN/m	Ultra-soft spring constant
Quality Factor (Q)	162,000	N/A	Highest measured Q (at 140 mK)
Dissipation (γ)	3.7	pg/s	γ = sqrt(km)/Q
Thermal Force Noise (F_th)	0.19	aN/√Hz	Record low achieved at 100 mK
Operating Temperature	100 - 150	mK	Cryogenic measurement regime

Key Methodologies

The nanoladder devices require precise, high-aspect-ratio patterning of thin-film Single Crystal Diamond (SCD) and specialized release techniques.

SCD Nanoladder Fabrication Process Flow

SCD Preparation:
- Initial material used: Electronic-grade Single Crystal Diamond (SCD) wafer.
- Thickness requirement: Material polished down to a thickness of 20 µm.
- Orientation: (100) surface used for patterning.
Patterning:
- Lithography: Electron Beam Lithography (EBL) was used to define the high-resolution nanoladder pattern (feature sizes ~100 nm).
Etching and Structuring:
- Pattern Transfer: The pattern was transferred into the SCD layer using Inductively Coupled Plasma (ICP) etching.
- Protection: Devices were intentionally designed to be tethered to the support substrate to protect the ultra-fragile nanoladder structure during the final release step.
Final Release and Post-Processing:
- Tether Removal: The protective tethers were severed using a highly localized Focused Helium Ion Beam (He-FIB).
- He-FIB Parameters: Operated at 30 kV acceleration voltage; beam current selected was 5 - 10 pA.
- Cut Depth: A dose of ~1 C/cm² resulted in a precise cut depth of 200 - 400 nm.
Measurement Readout Integration:
- A paddle (3 x 3 µm²) was fabricated near the cantilever tip to serve as a mirror for displacement detection.
- Detection utilized a fiber-optic interferometer operating at a wavelength of 1550 nm in a custom-built force microscope cooled by a dilution refrigerator (80 mK base temperature).

6CCVD Solutions & Capabilities: Enabling Next-Generation Quantum Sensors

The fabrication of these record-breaking nanomechanical resonators relies entirely on the precise control of crystal quality, thickness, surface finish, and microstructure—all core competencies of 6CCVD.

Applicable Materials

To replicate and extend this research towards commercial viability and improved performance (e.g., lower F_th via higher Q), 6CCVD recommends the following materials:

Ultra-Low Strain Optical Grade SCD: Essential for achieving Q factors in the hundreds of thousands (162,000 observed here) at cryogenic temperatures. Our MPCVD growth process yields electronic and optical grade SCD necessary to minimize intrinsic material dissipation (γ).
Custom Thin-Film SCD: The paper utilized 20 µm SCD. 6CCVD delivers custom-thickness SCD wafers ranging from 0.1 µm up to 500 µm. This capability is critical for optimizing the mass (m) and spring constant (k) needed to tune the resonant frequency (f_c) for specific MRFM or optomechanical requirements.
Boron-Doped Diamond (BDD): For applications requiring integrated electrical control or high conductivity at the sensor base, 6CCVD offers BDD thin films, providing a robust, highly conductive platform for complex chip integration.

Customization Potential

The constraints of fabricating fragile, nanometer-scale devices are perfectly addressed by 6CCVD’s advanced post-processing services:

Service	Requirement Identified in Paper	6CCVD Capability	Value Proposition
Custom Thickness	20 µm SCD wafers	SCD thicknesses from 0.1 µm to 500 µm	Enables optimal mass/spring constant tuning for force noise reduction.
High-Precision Polishing	Surface/Sidewall Roughness limits Q	Ra < 1 nm (SCD), Ra < 5 nm (PCD)	Minimizes surface adsorbates and sidewall roughness, crucial for maximizing cryogenic Q factors and reducing dissipation (γ).
Advanced Etching Prep	High-aspect-ratio features (~100 nm)	Custom material preparation for EBL/ICP processing	Facilitates repeatable, scalable etching recipes necessary for high-volume fabrication of nanoladder structures.
Metalization	Optical paddle (mirror) readout required	Internal deposition of Au, Pt, Ti, W, Cu layers	Allows for tailoring the optical properties (e.g., increased reflectivity) to reduce laser heating effects observed at 1550 nm, thereby lowering mode temperature (T) and further decreasing F_th.
Custom Dimensions	Device lengths of 100-300 µm	Plates/wafers up to 125 mm (PCD/SCD)	Supports engineering for larger arrays and batch processing necessary for commercialization of AFM/MRFM probes.

Engineering Support

The challenges noted in this research—specifically minimizing dissipation related to surface effects and optimizing material reflectivity for cryogenic operation—fall directly within our technical expertise.

6CCVD’s in-house PhD team provides consultative support specializing in material selection, orientation matching, and post-growth processing strategies (like surface chemical treatment mentioned in the paper) required to maintain ultra-high Q factors in nanomechanical systems. We are dedicated to accelerating research projects focused on Magnetic Resonance Force Microscopy (MRFM) and single nuclear spin detection, ensuring materials meet the stringent environmental and thermal demands of dilution refrigerator experiments.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

We present a “nanoladder” geometry that minimizes the mechanical dissipation of ultrasensitive cantilevers. A nanoladder cantilever consists of a lithographically patterned scaffold of rails and rungs with feature size ∼100 nm. Compared to a rectangular beam of the same dimensions, the mass and spring constant of a nanoladder are each reduced by roughly 2 orders of magnitude. We demonstrate a low force noise of 158-42+62 zN and 190-33+42 zN in a 1 Hz bandwidth for devices made from silicon and diamond, respectively, measured at temperatures between 100-150 mK. As opposed to bottom-up mechanical resonators like nanowires or nanotubes, nanoladder cantilevers can be batch-fabricated using standard lithography, which is a critical factor for applications in scanning force microscopy.

Tech Support

Original Source

DOI: https://doi.org/10.1021/acs.nanolett.7b05035