Polycrystalline Diamond Substrates Research Articles

Benchmarking diamond surface preparation and fluorination via inductively coupled plasma-reactive ion etching

Diamond, renowned for its exceptional semiconducting properties, stands out as a promising material for high-performance power electronics, optics, quantum, and biosensing technologies. This study methodically investigates the optimization of polycrystalline diamond (PCD) substrate surfaces through Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE). Various parameters, including gaseous species, flow rate, coil power, and bias power were tuned to understand their impact on surface morphology and chemistry. A thorough characterization, encompassing chemical, spectroscopic, and microscopic methods, shed light on the effects of different ICP-RIE conditions on surface properties. CF4/O2 plasma emerged as a viable treatment for achieving smooth PCD surfaces with minimal etch pit formation. Most notably, surface fluorination, a critical aspect of increasing chemical and thermal stability, was successfully accomplished using CF4, SF6, and other F-containing plasmas. The fluorine concentration and surface chemistry variations were studied, with high resolution X-ray Photoelectron Spectroscopy unveiling differences amongst the sp2 C phase, sp3 C phase, C–O, CO, and C–F bonds. Time-of-flight secondary Ion Mass Spectrometry (ToF-SIMS) and depth-profile analysis unveiled a consistent surface fluorination pattern with CF4/O2 treatment. Furthermore, contact angle measurements showcased heightened hydrophobicity. This study provides valuable insights into precise diamond surface engineering, important for the development of future diamond-based semiconductor technologies.

Heterogeneous integration of thick GaN and polycrystalline diamond at room temperature through dynamic plasma polishing and surface-activated bonding

Direct heterogeneous integration of GaN on diamond enhances device performance and reliability for high-power applications, while the implementation on thick GaN films and polycrystalline diamond (p-diamond) substrates remains challenging. In this study, the direct bonding between thick GaN films (∼370 μm) and p-diamond substrates was achieved. A dynamic plasma polishing (DPP) technique was adopted on the diamond to flatten surficial spikes from maximum 15 nm to 1.2 nm, obtaining a smooth surface with 0.29 nm Ra, achieving a robust GaN/diamond bonding with high bonding rate of ∼92% at room temperature combining the surface-activated bonding (SAB) method. The chemical status, thermal stress, and interfacial microstructures of GaN/diamond heterostructures were analyzed, revealing a residual stress of ∼200 MPa at the GaN/diamond interface, and the asymmetric increase of interfacial stress at rising temperature demonstrates the effectiveness of amorphous interlayer to release the stress.

The Influence of Site of Co and Holes in PCD Substrate on Adhesive Strength of Diamond Coating with PCD Substrate

Polycrystalline diamond (PCD) prepared by the high temperature and pressure method often uses Co as a binder, which had a detrimental effect on the cutting performance of PCD, thus Co needed to be removed. However, the removal of Co would cause residual holes and also make the cutting performance of PCD poorer. To address this issue, hot filament chemical vapor deposition (HFCVD) was used. During deposition, the residual holes cannot be filled fully, and Co would diffuse to the interface between CVD diamond coatings and the PCD substrate, which influenced the adhesive strength of the diamond coating with the PCD substrate. In order to investigate the influencing mechanism, both experiments and the density functional theory (DFT) calculations have been employed. The experimental results demonstrate that Co and the holes in the interface would reduce the interfacial binding strength. Further, we built interfacial structures consisting of diamond (100), (110), (111) surfaces and PCD to calculate the corresponding interfacial binding energy, charge density and charge density difference. After contrast, for Co and the holes located on the (110) surface, the corresponding interfacial binding energy was bigger than the others. This means that the corresponding C-C covalent bond was stronger, and the interfacial binding strength was higher. Based on this, conducting cobalt removal pretreatment, optimizing the PCD synthetic process and designing the site of Co can improve the performance of the PCD substrate CVD diamond coating tools.

Thermal effect of Nd:YAG bonded on diamond by Mo/Au metal intermediate layer at room temperature

To overcome the thermal effect of a Nd:yttrium aluminum garnet (YAG) disk, a polycrystalline diamond substrate is successfully bonded to the Nd:YAG disk using a Mo/Au interlayer at room temperature. The results show that the Nd:YAG disk and diamond are almost completely bonded, with some voids at the edge of the bonding layer. Scanning electron microscopy analysis shows that the bonding interface with a thickness of 143 nm is continuous and free of nanodefects. In addition, a numerical model is developed to analyze the thermodynamic properties of the Nd:YAG/diamond composite structure. The analytical results show that a diamond heat sink significantly reduces thermal aberration compared with Cu and SiC heat sinks. Furthermore, the bending optical path difference (OPD) is proved to be a major component of the total OPD. This study is expected to help realize diamond-based laser systems with high-power output.

Control morphology and properties in additive manufacturing of functional gradient cemented carbides for polycrystalline diamond substrates

Cemented carbide substrates contribute mainly to the strength and impact toughness of polycrystalline diamond composites (PDC). By using a PW-MW-HDPE-EVA-SA mixed polymeric binder and combining Powder Extrusion Printing (PEP) with densification sintering processes, the YG10/YG15 functionally gradient cemented carbides (FGCCs) with different powder loadings were prepared. This study focuses on exploring process feasibility and the integrated regulatory mechanisms for FGCCs morphology and performance. The results showed that the configured cemented carbide feedstocks with different powder loadings exhibited uniform composition and good shear-thinning characteristics, making them suitable for extrusion printing. The FGCC green parts formed by PEP have macro-structurally intact, dense surfaces and uniformly stacked extrusion filaments with a roughness of 12.25 μm. After degreasing and sintering, FGCCs with densities exceeding 99.43% were obtained. The shrinkage and Co gradient distribution of the inner and outer layers were regulated by powder loading design, achieving integrated control of FGCCs morphology and properties. With powder loading increase in YG15, the density of FGCCs remained stable between 14.01 and 14.03 g/cm3, the gradient dimensions difference decreased from 14.34% to 7.9%, and the maximum hardness difference increased from 78 to 121 HV1/15.

Understanding of the adhesive strength enhancement mechanisms of bilayer diamond film at nanoscale

In virtue of its outstanding comprehensive performances, the development of multilayer diamond holds significant potential for expanding the range of applications for diamond. However, there still is a major challenge to synthesize multilayer diamond with high adhesive strength. In this work, a bilayer diamond film with enhanced adhesive strength was successfully prepared through depositing nanocrystalline diamond film on plasma-etched polycrystalline diamond substrate using chemical vapor deposition. The adhesion strength was evaluated by the critical load when film failed during scratch test. The nanocrystalline diamond film deposited on plasma-etched substrate exhibited a critical load of 121.6 N, which is higher by 57 % than that deposited on substrate without plasma etching. TEM observation demonstrated that the nanocrystalline diamond has a preference for nucleating at the bottom of pits on the substrate produced by plasma etching, constructing a unique interface with a mortise and tenon joint structure. Moreover, Raman results verified the removal of the graphite phase in substrate surface during plasma etching. Our findings reveal the mechanisms responsible for the enhanced adhesive strength of the developed bilayer diamond film at nanoscale. The improved adhesive strength can be attributed to the combination of the mechanical interlocking interface and the removal of the graphite phase. In addition, the method presented in this work can also be employed on chemical vapor deposition of other multilayer materials beyond diamond, offering the potential to enhance their adhesive strength.

Nucleation of cubic boron nitride on boron-doped diamond via plasma enhanced chemical vapor deposition

Cubic boron nitride (c-BN), with a small 1.4% lattice mismatch with diamond, presents a heterostructure with multiple opportunities for electronic device applications. However, the formation of c-BN/diamond heterostructures has been limited by the tendency to form hexagonal BN at the interface. In this study, c-BN has been deposited on free standing polycrystalline and single crystal boron-doped diamond substrates via electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD), employing fluorine chemistry. In situ x-ray photoelectron spectroscopy (XPS) is used to characterize the nucleation and growth of boron nitride (BN) films as a function of hydrogen gas flow rates during deposition. The PECVD growth rate of BN was found to increase with increased hydrogen gas flow. In the absence of hydrogen gas flow, the BN layer was reduced in thickness or etched. The XPS results show that an excess of hydrogen gas significantly increases the percent of sp2 bonding, characteristic of hexagonal BN (h-BN), particularly during initial layer growth. Reducing the hydrogen flow, such that hydrogen gas is the limiting reactant, minimizes the sp2 bonding during the nucleation of BN. TEM results indicate the partial coverage of the diamond with thin epitaxial islands of c-BN. The limited hydrogen reaction is found to be a favorable growth environment for c-BN on boron-doped diamond.

High Performance of Normally‐On and Normally‐Off Devices with Highly Boron‐Doped Source and Drain on H‐Terminated Polycrystalline Diamond

AbstractDiamond exhibits large application potential in the field of power electronics, owing to its excellent and desirable electronic properties. However, the main obstacles to its development originate from the small‐sized single‐crystal wafers and the instability of the electrical conductivity. This work presents a metal‐oxide‐semiconductor field‐effect transistor (MOSFET) on a diamond substrate derived from a five‐inch (110) highly preferred polycrystalline diamond film. The MOSFETs with excellent performance are fabricated by combining an H‐terminated channel and an epitaxially grown boron‐doped layer as the source/drain contacts of the diamond devices. According to the electrical statistical results of ≈110 devices on the polycrystalline diamond substrate, 44% of devices show normally‐off operation with a maximum current density of 400 mA mm−1, while 56% of devices demonstrate normally‐on operation with a maximum current density of 525 mA mm−1. The normally‐off characteristics are more related to the higher amounts of nitrogen concentration than the grain boundaries. The stable boron‐doped source and drain provide a high concentration of holes, which facilitate transport in the surface p‐type channel induced by the H‐termination. The characteristics of the MOSFETs are inspiring for the fabrication of complementary inverter circuits on large diamond wafers.

Design and Comparison of Diamond‐ and Sapphire‐Based NbN KIDs for Fusion Plasma Polarimetric Diagnostics

Design and characterization measurements performed on kinetic inductance detectors (KIDs) produced on sapphire and polycrystalline diamond substrates are presented. Designed as part of a nuclear fusion polarimetric diagnostic, the foreseen plasma‐probing frequency of the final devices is 1.3 THz with a maximum response time under 10 ms and cross‐polarization target accuracy of 1%. These detectors are based on superconducting micro‐resonators that undergo de‐tuning upon absorption of radiation. The main characteristics of the devices include polarization sensitiveness and lumped‐elements multi‐pixel configuration produced from photo‐lithographed niobium nitride (NbN) thin films. The direct current (DC) and microwave characterization measurements highlight large differences in the thin film quality, with the superconductor deposited on diamond showing reduced critical temperature, lower critical current density, and increased values of the kinetic inductance. This difference is likely due to the higher lattice constant and thermal expansion coefficient mismatch between film and substrate in the case of diamond, with the different surface finish quality of the crystalline samples available also playing a role. The devices on both substrates show a bolometric response to THz radiation that fulfills the requirement guidelines and represent a good starting point to optimize the design for the application at hand.

SAW Resonators and Filters Based on Sc0.43Al0.57N on Single Crystal and Polycrystalline Diamond.

The massive data transfer rates of nowadays mobile communication technologies demand devices not only with outstanding electric performances but with example stability in a wide range of conditions. Surface acoustic wave (SAW) devices provide a high Q-factor and properties inherent to the employed materials: thermal and chemical stability or low propagation losses. SAW resonators and filters based on synthetized by reactive magnetron sputtering on single crystal and polycrystalline diamond substrates were fabricated and evaluated. Our SAW resonators showed high electromechanical coupling coefficients for Rayleigh and Sezawa modes, propagating at 1.2 GHz and 2.3 GHz, respectively. Finally, SAW filters were fabricated on /diamond heterostructures, with working frequencies above 4.7 GHz and ~200 MHz bandwidths, confirming that these devices are promising candidates in developing 5G technology.

Polarization‐Driven‐Orientation Selective Growth of Single‐Crystalline III‐Nitride Semiconductors on Arbitrary Substrates (Adv. Funct. Mater. 14/2022)

Arbitrary Substrates In article number 2113211, Xuelin Yang, Bing Huang, Bo Shen, and co-workers propose a strategy of polarization-driven-orientation selective growth and demonstrate that single-crystalline GaN can in principle be achieved on polycrystalline diamond or other substrates by utilizing a composed buffer layer consisting of graphene and polycrystalline physical-vapor-deposited AlN. This strategy can be extended to the growth of any emergent single-crystalline semiconductor films on any arbitrary freestanding substrates by choosing appropriate 2D materials with matched crystal structures.

Accelerating double pulse all-optical write/erase cycles in metallic ferrimagnets

All-optical switching of magnetic order presents a promising route toward faster and more energy efficient data storage. However, a realization in future devices is ultimately dependent on the maximum repetition rates of optically induced write/erase cycles. Here, we present two strategies to minimize the temporal separation of two consecutive femtosecond laser pulses to toggle the out-of-plane direction of the magnetization of ferrimagnetic rare-earth transition metal alloys. First, by systematically changing the heat transfer rates using either amorphous glass, crystalline silicon, or polycrystalline diamond substrates, we show that efficient cooling rates of the magnetic system present a prerequisite to accelerate the sequence of double pulse toggle switching. Second, we demonstrate that replacing the transition metal iron by cobalt leads to a significantly faster recovery of the magnetization after optical excitation allowing us to approach terahertz frequency of write/erase cycles with a minimum pulse-to-pulse separation of 7 ps.

Wafer-Scale Polishing of Polycrystalline MPACVD-Diamond

Diamond offers great potential for use as a thermal spreader in various applications, including power electronics and radio-frequency (RF) applications. However, to be used as an efficient thermal spreader, the atomically smooth surface of the diamond is critical to be bonded with chips. Herein, a polishing technique for a 2-inch diameter wafer-scale bulk polycrystalline diamond substrate is proposed. In this work, 350 μm thick polycrystalline diamond is grown by the microwave plasma-assisted chemical vapor deposition (MPACVD) technique on a Si substrate at a growth rate of 8 µm/h. Thereafter, a three-step polishing process was applied to achieve an atomically smooth surface, consisting of grinding using a diamond slurry with an iron plate, ICP etching using the SF6 gas, and final mechanical polishing using a resin-bonded diamond wheel. Surface roughness of diamond characterized by atomic force microscopy showed the significantly reduced from 900 nm to 0.3 nm. Hence, this study provide the practical methods for obtaining atomically smooth diamond films suitable for thermal management in various areas including power electronics and RF devices.

Investigation of Laser-Induced Periodic Surface Structures Using Synthetic Optical Holography.

In this paper, the investigation of laser-induced periodic surface structures (LIPSSs) on a polycrystalline diamond substrate using synthetic optical holography (SOH) is demonstrated. While many techniques for LIPSS detection operate with sample contact and/or require preparation or processing of the sample, this novel technique operates entirely non-invasively without any processing of or contact with the LIPSS sample at all. The setup provides holographic amplitude and phase images of the investigated sample with confocally enhanced and diffraction-limited lateral resolution, as well as three-dimensional surface topography images of the periodic structures via phase reconstruction with one single-layer scan only.

Simulation research on nucleation mechanism of graphene deposition assisted by diamond grain boundary

The growth of high-quality graphene is always a focused issue in the field of two-dimensional materials, and the growth of graphene on brand new substrates has received considerable attention from scholars especially. The research on the nucleation mechanism of graphene deposited on a polycrystalline diamond substrate is of significance in the large-scale preparation of graphene in practice. Here in this work, the direct growth without transfer process of graphene on a diamond substrate is used to obtain the high-quality graphene. The reactive molecular dynamics simulation technology is adopted to imitate the process of graphene deposition and growth on bi-crystal diamond assisted by nickel catalyzed at an atomic level. The effect of the bi-crystal diamond grain boundary on the dynamic behavior of graphene nucleation and growth process is studied. The results demonstrate that the grain boundary carbon atoms can be used as a supplementary carbon source to diffuse into the nickel free surface and participate in the nucleation and growth of graphene. Furthermore, the effect of temperature on the diffusion behavior of carbon atoms is explored, finding that high temperature facilitates the dissociation of atoms in the grain boundary. When the deposition temperature equals 1700 K, it is most conducive to the diffusion of grain boundary carbon atoms in the nickel lattice, which effectively enhances the nucleation density of graphene. Besides, the effect of the deposition carbon source flow rate on the surface quality of graphene is explored, finding that the high-quality graphene surface can be obtained by adopting a lower carbon deposit rate of 1 ps<sup>–1</sup> at 1700 K. In brief, the research results obtained not only provide an effective theoretical model and analysis of the mechanism for diamond grain boundary assisted graphene deposition and growth, but also reveal the regular pattern of influence of deposition temperature and deposition carbon source flow rate on the surface quality of synthesized graphene. The present study can lay a theoretical foundation for the fabrication and application of new functional graphene-polycrystalline diamond heterostructures in the fields of ultra-precision manufacturing and microelectronics.

Efficiency of Photoconductive Terahertz Generation in Nitrogen-Doped Diamonds

The efficiency of the generation of terahertz radiation from nitrogen-doped (∼0.1–100 ppm) diamonds was investigated. The synthetic polycrystalline and monocrystalline diamond substrates were pumped by a 400 nm femtosecond laser and tested for the photoconductive emitter operation. The dependency of the emitted THz power on the intensity of the optical excitation was measured. The nitrogen concentrations of the diamonds involved were measured from the optical absorbance, which was found to crucially depend on the synthesis technique. The observed correlation between the doping level and the level of the performance of diamond-based antennas demonstrates the prospects of doped diamond as a material for highly efficient large-aperture photoconductive antennas.

Spatially selective, solid state etching of diamond using lithographically patterned FeCoB

Nanocrystalline layers of FeCoB (Fe:Co:B = 60:20:20 at atom ratio) enable spatially selective, microstructurally agnostic removal of diamond through a solid-state diffusion reaction. Lithographically fabricated 100-300 nm thick films of FeCoB are deposited on polycrystalline diamond substrates. Heat treatment at temperatures ranging from 700 °C–900 °C for 30 min–90 min are used to trigger the conversion of sp3 to sp2 carbon at the diamond-transition metal interface. The integrity of the solid-state etchant within the thermal processing window underpins the spatial selectivity with which the diamond is removed. Removal of the reaction products using solvothermal etching in an acid solution enables the recovery of the structured diamond surfaces. FeCoB offers material removal rates, which exceeds that possible with just Fe or Co – pointing to the key role of B. The interaction zone was excised using focused ion beam milling and characterized using electron microscopy. In addition, XRD and Raman spectroscopy were performed to study the phase composition of the interaction zone. The role of the transition metal-diamond interface is key to controlling the material removal; the stability of the interface determines the ability to faithfully replicate the ultrafine features that were lithographically patterned in the FeCoB.

High quality GaN grown on polycrystalline diamond substrates with h-BN insertion layers by MOCVD

The single crystal GaN film was successfully grown on the polycrystalline diamond substrate using a h-BN insertion layer by metal–organic chemical vapor deposition, which solved the problem that GaN and diamond are difficult to combine due to the lattice and thermal mismatch. After using h-BN and optimizing the growth process of AlN nucleation layer, the full width at half maximum value of (002) plane of GaN is decreased from 4.67° to 1.20°. The root mean square roughness is decreased from 31.5 nm to 1.07 nm, and the yellow luminescence caused by carbon impurity is obviously suppressed. The successful preparation of single crystal GaN film on polycrystalline diamond provides a new solution for the heat dissipation problem, which has plagued the development of GaN-based power devices for a long time.

Effect of GaN-on-diamond integration technology on its thermal properties

Two different integration technologies of GaN-on-diamond are explored, direct growth of polycrystalline diamond (PCD) on GaN (sample A) and deposition of GaN on PCD (sample B). The reversed evolution of PCD grain structure is assumed for each technology, resulting in an increasing/decreasing tendency of thermal conductivity with growth thickness. Simulation of AlGaN/GaN high electron mobility transistors on PCD substrate with capped diamond is made considering anisotropic and inhomogeneous thermal conductivities of GaN and PCD, different combinations of thermal boundary resistance (TBR) values at the top diamond/GaN and bottom GaN/PCD substrate are investigated. The results show that the effect of top TBR is limited and increasing the bottom TBR from 6.5 to 100 m2K GW−1 results in a temperature rise of 80.8 °C for sample A and 85.3 °C for sample B at power dissipation of 10 W mm−1. Enlarging the thickness of capped diamond helps to reduce the junction temperature, which is more effective at small top TBR under constant bottom TBR and at large bottom TBR with fixed top TBR. In addition, increasing gate pitch is a promising solution to reduce junction temperature and a weak dependence of junction temperature on gate width is revealed.

High frequency hydrogen-terminated diamond MESFET with an fmax of 103GHz

High-quality polycrystalline diamond substrate was used to fabricate diamond MESFETs by a self-aligned process. The fabricated diamond MESFETs with a gate length of 130 nm show good direct current and radio frequency performances, with the maximum saturation source-drain current IDS of 560 mA/mm, the Ion/Ioff ratio of 107, the transconductance of 225 mS/mm, and the current gain cut-off frequency fT of 40.7 GHz and the maximum oscillation frequency fmax of 103 GHz. These results show that the high-quality polycrystalline freestanding diamond is a promising candidate for the investigation of high frequency electronic devices.