Mechanical and Electrical Properties of Free‐standing Polycrystal Diamond Membranes
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-06-28 |
| Journal | Advanced Science |
| Authors | Chenyu Wang, Dmitry Shinyavskiy, L. J. Suter, Zubaida Altikriti, Q. X. Jia |
| Institutions | University at Buffalo, State University of New York, Fraunhofer USA |
| Citations | 1 |
| Analysis | Full AI Review Included |
Technical Analysis and Documentation: Free-standing Polycrystalline Diamond Membranes (PCDm)
Section titled “Technical Analysis and Documentation: Free-standing Polycrystalline Diamond Membranes (PCDm)”Executive Summary
Section titled “Executive Summary”This research validates the potential of free-standing, transferable Polycrystalline Diamond Membranes (PCDm) synthesized via Microwave Plasma-Enhanced Chemical Vapor Deposition (MPCVD). The findings directly support 6CCVD’s expertise in high-quality, customizable PCD materials for advanced electronic and mechanical applications.
- Ultra-High Elastic Modulus: PCDm cantilevers exhibited an elastic modulus (E) ranging from 911 GPa to 1014 GPa, demonstrating minimal mechanical degradation and approaching the stiffness of bulk Single Crystal Diamond (SCD) (≈1130 GPa).
- Surface-Dependent Properties: Two orientations were tested: Top-Surface-Up (TSU) and Bottom-Surface-Up (BSU). BSU-PCDm utilized the smoother growth interface, resulting in superior surface quality (10x smoother) and stable electrical resistance under strain.
- Boron Doping Effects: Boron incorporation was concentrated near the top surface (TSU), leading to a lower bandgap (Eg ≈ 3.31 eV) compared to the BSU surface (Eg ≈ 3.98 eV), confirming tunability via doping profile control.
- Strain-Stable Electronics: BSU-PCDm maintained a stable sheet resistance (49.7 Ω sq-1) under mechanical strain, making it ideal for flexible, high-performance electronic devices and sensors.
- Scalability and Transferability: The method enables the creation of free-standing, transferable membranes, overcoming the size and integration limitations typically associated with conventional PCD thin films.
- Target Applications: The material is positioned as a strong candidate for cost-effective, high-performance power electronics, UV photodetectors, and biocompatible sensors.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the analysis of the PCDm cantilevers:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Film Thickness | 3.8 | µm | MPCVD Boron-Doped Diamond |
| Long Cantilever Dimensions | 300 x 2000 | µm | Width x Length |
| Short Cantilever Dimensions | 150 x 1200 | µm | Width x Length |
| Elastic Modulus (TSU, Long) | 1014 | GPa | Top-Surface-Up PCDm (Highest E) |
| Elastic Modulus (BSU, Long) | 911 | GPa | Bottom-Surface-Up PCDm |
| Bandgap (TSU, XPS) | 3.31 | eV | Attributed to Boron incorporation |
| Bandgap (BSU, XPS) | 3.98 | eV | Attributed to increased Hydrogen content |
| Sheet Resistance (BSU, Flat) | 49.7 | Ω sq-1 | Stable under strain |
| Sheet Resistance (TSU, Flat) | 60.19 | Ω sq-1 | Decreases under compressive strain |
| Bottom Surface Grain Size | ≈500 | nm | Smoother surface |
| Top Surface Grain Size | ≈1200 | nm | Rougher, mushroom-like growth |
| PCD Thermal Conductivity (Reference) | Up to 1800 | W K-1m-1 | Bulk PCD property |
Key Methodologies
Section titled “Key Methodologies”The free-standing PCDm cantilevers were fabricated using a combination of MPCVD growth, micro-fabrication, and selective etching techniques:
- Growth Method: Boron-doped diamond film was grown using Microwave Plasma-Enhanced Chemical Vapor Deposition (MPECVD).
- Substrate Preparation: (100) Si/SiO2 wafers were scratch-seeded for 5 minutes using 0-2 µm diamond powder to promote nucleation density.
- CVD Parameters:
- Pressure: 60 Torr.
- Forward Power: 7 kW.
- Temperature: 936 °C.
- Gas Mixture: 8 sccm CH4, 385 sccm H2, and 7.5 sccm B2H6 (Boron Doping).
- Patterning Mask: A bi-layered metal stack of Cr (100 nm) / Ni (300 nm) was deposited via E-beam evaporation to serve as an etching mask.
- Etching: Inductively Coupled Plasma - Reactive Ion Etching (ICP-RIE) was used to define the cantilever patterns (150 µm and 300 µm widths).
- Release: The patterned PCD layer was released from the Si substrate by immersing the sample in Hydrofluoric (HF, 49%) acid to dissolve the underlying SiO2 layer.
- Transfer: Released PCDm cantilevers were transferred onto an SU-8 coated Si wafer using a micro-transfer printing technique, allowing for selective orientation (TSU or BSU).
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”This research demonstrates the critical need for highly controlled MPCVD diamond growth, precise doping, and advanced micro-structuring—all core competencies of 6CCVD. We are uniquely positioned to replicate and scale this technology for commercial and research applications.
Applicable Materials
Section titled “Applicable Materials”To replicate or extend the research on strain-stable, high-modulus PCDm, 6CCVD recommends the following materials:
- Heavy Boron-Doped Polycrystalline Diamond (BDD PCD): Essential for achieving the conductive properties (Rs < 61 Ω sq-1) and tunable bandgaps (3.31 eV to 3.98 eV) demonstrated in the study. 6CCVD offers precise control over B2H6 flow rates to tailor conductivity and doping profiles throughout the film thickness.
- Optical Grade PCD: For applications requiring the superior smoothness of the BSU surface (which replicates the substrate), 6CCVD guarantees Polishing to Ra < 5 nm on inch-size PCD wafers, ensuring the required low roughness for subsequent device integration or optical clarity.
- Ultra-Thin SCD/PCD Films: The paper utilized a 3.8 µm film. 6CCVD routinely delivers thin films in the range of 0.1 µm to 500 µm, allowing researchers to explore the mechanical and electrical limits of even thinner, more flexible membranes.
Customization Potential
Section titled “Customization Potential”The fabrication of PCDm cantilevers requires precise geometry definition and multi-layer processing. 6CCVD offers comprehensive customization services:
| Research Requirement | 6CCVD Capability | Benefit to Client |
|---|---|---|
| Custom Dimensions (150 µm, 300 µm wide beams) | Custom Laser Cutting & Etching: Precise patterning of plates/wafers up to 125mm in diameter. | Enables rapid prototyping and scalable production of complex MEMS/NEMS structures (e.g., cantilevers, diaphragms). |
| Metalization (Cr/Ni mask, Al contacts) | Internal Metalization Services: Deposition of standard (Au, Pt, Ti) and specialized (W, Pd, Cu) metal stacks. | Facilitates the integration of electrical contacts (TLM patterns) and etching masks directly onto the diamond film, streamlining the fabrication process. |
| Thickness Control (3.8 µm film) | Thickness Precision: SCD/PCD films available from 0.1 µm up to 500 µm. | Allows researchers to systematically vary film thickness to optimize mechanical flexibility and strain response for specific sensor or actuator designs. |
| Transfer Substrates (Si/SiO2, SU-8) | Substrate Flexibility: Growth on various substrates (Si, SiC, etc.) and custom transfer onto foreign platforms. | Supports the development of heterogeneous integration, crucial for the transferable PCDm concept demonstrated in the paper. |
Engineering Support
Section titled “Engineering Support”The differences observed between the TSU and BSU surfaces—driven by grain size, defect distribution, and boron/hydrogen content—highlight the complexity of controlling MPCVD growth for specific device requirements.
- Process Optimization: 6CCVD’s in-house PhD engineering team specializes in optimizing MPCVD growth recipes to control critical material parameters, such as:
- Doping Profile: Tuning BDD concentration to achieve specific bandgap and conductivity targets for power electronics or UV photodetectors.
- Crystallinity and Surface Morphology: Adjusting growth parameters to minimize sp2 content and control grain size, ensuring the desired mechanical stiffness and surface smoothness (e.g., replicating the smooth BSU surface).
- Strain Engineering: Assisting clients in selecting the optimal material orientation (TSU vs. BSU) and doping level to achieve either strain-sensitive or strain-stable electrical properties for advanced sensor applications.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract In this study, we demonstrate a novel approach for synthesizing free‐standing and transferable polycrystalline diamond membranes (PCDm) to overcome these constraints, thus enabling a much wider spectrum of applications. Two types of PCDm cantilevers —Top‐Surface‐Up (TSU) and Bottom‐Surface‐Up (BSU) are fabricated, each with two different sets of dimensions: 150 µm (width) × 1200 µm (length) and 300 µm (width) × 2000 µm (length). Their mechanical and electrical properties are systematically investigated. Atomic Force Microscopy (AFM) analysis revealed that TSU‐PCDm has a higher elastic modulus than BSU‐PCDm, attributed to differences in grain size and defect distribution. Despite these differences, all PCDms in our work exhibit consistently high modulus values with minimal mechanical degradation across various cantilever geometries. Bandgap measurements using X‐ray Photoelectron Spectroscopy (XPS) and UV-vis absorption spectroscopy indicated a lower bandgap for TSU‐PCDm due to boron incorporation, while BSU‐PCDm exhibited a higher bandgap due to increased hydrogen content. Electrical characterization showed that the sheet resistance of TSU‐PCDm decreases under strain, whereas BSU‐PCDm maintains stable resistance. These findings unveil the material properties of PCDm and their potential usage for myriad diamond‐based electronic applications.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
Section titled “References”- 2015 - Traditional Machining Processes: Research Advances