Microelectromechanical Systems Materials Research Articles

A high aspect ratio surface micromachined accelerometer based on a SiC-CNT composite material

Silicon carbide (SiC) is recognized as an excellent material for microelectromechanical systems (MEMS), especially those operating in challenging environments, such as high temperature, high radiation, and corrosive environments. However, SiC bulk micromachining is still a challenge, which hinders the development of complex SiC MEMS. To address this problem, we present the use of a carbon nanotube (CNT) array coated with amorphous SiC (a-SiC) as an alternative composite material to enable high aspect ratio (HAR) surface micromachining. By using a prepatterned catalyst layer, a HAR CNT array can be grown as a structural template and then densified by uniformly filling the CNT bundle with LPCVD a-SiC. The electrical properties of the resulting SiC-CNT composite were characterized, and the results indicated that the electrical resistivity was dominated by the CNTs. To demonstrate the use of this composite in MEMS applications, a capacitive accelerometer was designed, fabricated, and measured. The fabrication results showed that the composite is fully compatible with the manufacturing of surface micromachining devices. The Young’s modulus of the composite was extracted from the measured spring constant, and the results show a great improvement in the mechanical properties of the CNTs after coating with a-SiC. The accelerometer was electrically characterized, and its functionality was confirmed using a mechanical shaker.

Characterization of Photocurable IP-PDMS for Soft Micro Systems Fabricated by Two-Photon Polymerization 3D Printing.

Recent developments in micro-scale additive manufacturing (AM) have opened new possibilities in state-of-the-art areas, including microelectromechanical systems (MEMS) with intrinsically soft and compliant components. While fabrication with soft materials further complicates micro-scale AM, a soft photocurable polydimethylsiloxane (PDMS) resin, IP-PDMS, has recently entered the market of two-photon polymerization (2PP) AM. To facilitate the development of microdevices with soft components through the application of 2PP technique and IP-PDMS material, this research paper presents a comprehensive material characterization of IP-PDMS. The significance of this study lies in the scarcity of existing research on this material and the thorough investigation of its properties, many of which are reported here for the first time. Particularly, for uncured IP-PDMS resin, this work evaluates a surface tension of 26.7 ± 4.2 mN/m, a contact angle with glass of 11.5 ± 0.6°, spin-coating behavior, a transmittance of more than 90% above 440 nm wavelength, and FTIR with all the properties reported for the first time. For cured IP-PDMS, novel characterizations include a small mechanical creep, a velocity-dependent friction coefficient with glass, a typical dielectric permittivity value of 2.63 ± 0.02, a high dielectric/breakdown strength for 3D-printed elastomers of up to 73.3 ± 13.3 V/µm and typical values for a spin coated elastomer of 85.7 ± 12.4 V/µm, while the measured contact angle with water of 103.7 ± 0.5°, Young's modulus of 5.96 ± 0.2 MPa, and viscoelastic DMA mechanical characterization are compared with the previously reported values. Friction, permittivity, contact angle with water, and some of the breakdown strength measurements were performed with spin-coated cured IP-PDMS samples. Based on the performed characterization, IP-PDMS shows itself to be a promising material for micro-scale soft MEMS, including microfluidics, storage devices, and micro-scale smart material technologies.

A DFT analysis on the superlubricity performance of structural superlubricity micro/nano-component on silicon-based surface

Friction and wear are important factors which limit the development of Micro-electromechanical Systems (MEMS). Therefore, the research and preparation of wear-resistant micro and nano-functional structures in the field of MEMS has profound importance. Structural superlubricity micro/nano-components (the atomic layers are in incommensurate contact, which means that the friction and wear rate is nearly zero when the layers slide) are expected to be the basic micro and nano functional structures for fabricating ultra wear-resistant MEMS. At present, there is a lack of research on the properties of structural superlubricity micro/nano-components on the surface of silicon, which is known to be the most mainstream base material for MEMS. In this paper, the electronic properties and the atomic-scale friction of the silicon-based surface structural superlubricity micro/nano-components are simulated using first-principles calculations based on the Density functional theory (DFT). By analyzing the silicon-based surface structural superlubricity micro/nano-component with adhesion performances and superlubricity characteristics. The calculation shows that the binding energy value of its lower graphene layer is larger than that of the upper layer during the slip process, and it is found that the friction force of the silicon-based structure can reach the range of 10−3 nN and the average friction coefficient can reach the range of 10−3 in the incommensurate state. Throughout the sliding process, electrostatic repulsion plays an important role in the tribological properties. The larger the electrostatic repulsion, the smoother the potential energy fluctuation, indicating less friction, while the analysis of the charge mechanism further justifies the conclusion.

4H-Silicon Carbide as an Acoustic Material for MEMS.

This paper discusses the potential of 4H-SiC as a superior acoustic material for MEMS, particularly for high-performance resonator and extreme environments applications. Through a comparison of the crystalline structure along with the mechanical, acoustic, electrical, and thermal properties of 4H with respect to other SiC polytypes and silicon, it is shown that 4H-SiC possesses salient properties for MEMS applications, including its transverse isotropy and small phonon scattering dissipation. The utility and implementation of bonded SiC on insulator (4H-SiCOI) substrates as an emerging MEMS technology platform are presented. Additionally, this paper reports on the temperature-dependent mechanical properties of 4H-SiC, including the temperature coefficient of frequency and quality factor for Lame mode resonators. Finally, the 4H-SiC MEMS fabrication including its deep reactive ion etching is discussed. This paper provides valuable insights into the potential of 4H-SiC as a mechano-acoustic material and provides a foundation for future research in the field.

Multimode TED-tuned beam mass damper for low-g capacitive MEMS accelerometers VRE reduction

Capacitive Micro-Electro-Mechanical Systems (MEMS) accelerometers for quasi-static applications are susceptible to vibration rectification error (VRE) when the ambient AC vibration signals get rectified to DC. Studies to mitigate the VRE have relied on the sigma-delta filtering algorithm with closed-loop feedback as well as the adoption of vibration-insensitive frequency modulation (FM) instead of conventional amplitude modulation. In this study, we propose a novel solution to VRE caused by asymmetric railing introducing multimode thermoelastic damping (TED) tuned beam mass damper (TBMD) integrated into the MEMS accelerometer effectively functioning as a compensator. Our contribution breaks through the microfabrication limitation of damping elements by utilizing intrinsic TED in MEMS material. The damper elements were alternately tuned up to the third flexural mode due to MEMS manufacturing constraints. This was done through parametric sweeps in numerical simulations on single-axis capacitive MEMS accelerometer integrated with multimode TED-damped TBMD. According to simulation results, the higher the mode shapes of the TED-damped tuned beam mass damper, the higher the damping effect and the better the vibration rectification factor.

Enhanced stimulated Brillouin scattering in the unsuspended silicon waveguide assisted with genetic algorithms.

Stimulated Brillouin scattering (SBS), originating from the coupling between optical and acoustic waves, has been widely applied in many fields. Silicon is the most used and important material in micro-electromechanical systems (MEMS) and integrated photonic circuits. However, strong acoustic-optic interaction in silicon requires mechanical release of the silicon core waveguide to avoid acoustic energy leakage into the substrate. This will not only reduce the mechanical stability and thermal conduction, but also increase the difficulties for fabrication and large-area device integration. In this paper, we propose a silicon-aluminium nitride(AlN)-sapphire platform for realizing large SBS gain without suspending the waveguide. AlN is used as a buffer layer to reduce the phonon leakage. This platform can be fabricated via the wafer bonding between silicon and commercial AlN-sapphire wafer. We adopt a full-vectorial model to simulate the SBS gain. Both the material loss and the anchor loss of the silicon are considered. We also apply the genetic algorithm to optimize the waveguide structure. By limiting the maximum etching step number to two, we obtain a simple structure to achieve the SBS gain of 2462 W-1m-1 for forward SBS, which is 8 times larger than the recently reported result in unsuspended silicon waveguide. Our platform can enable Brillouin-related phenomena in centimetre-scale waveguides. Our findings could pave the way toward large-area unreleased opto-mechanics on silicon.

KNN lead-free piezoelectric films grown by sputtering

Potassium sodium niobate [(K,Na)NbO3, KNN] films are promising lead-free piezoelectric materials for microelectromechanical systems (MEMS) devices. We previously developed technologies for forming high-quality KNN films by sputtering, which showed excellent piezoelectric properties comparable to lead zirconate titanate (PZT) films. In the present study, we addressed several challenges with the aim of introducing KNN films into commercialized MEMS devices. First, we optimized the dielectric and piezoelectric properties to realize a suitable performance for actuator and sensor devices. The sensor-type KNN films had a low dielectric constant (248) and a self-poling function, which are greatly beneficial for sensor device performance and the fabrication process. The actuator-type KNN films had a very high e31 value of −13.5 C/m2, which is almost comparable to the top level of PZT films. Next, we found that the DC stress lifetime of KNN films strongly depended on the material used for the adhesion layer of the top electrode. When we used a Pt/RuO2 top electrode, the actuator-type KNN films had a long lifetime (>130 000 s, 300 kV/cm and 200 °C), which is long enough to be used for commercialized MEMS devices. Furthermore, we realized 8-in. KNN wafers with good thickness uniformity across the wafer (±3.5%) by introducing a mass-production-ready sputtering tool: the EB-2500 produced by Canon Anelva. In the near future, these promising results will open the way to replace PZT with KNN in the piezoMEMS industry.

Advances in Graphene Based MEMS and Nems Devices: Materials, Fabrication, and Applications

Microelectromechanical systems (MEMS) are generally known as miniaturized mechanical and electro-mechanical systems, whereas NEMS stands for nanoelectromechanical systems. Graphene is an atomically thin material that features unique properties, such as high carrier mobility, high mechanical strength, and piezoresistive electromechanical transduction, which makes it an extremely promising material for future MEMS and NEMS devices. Design and fabrication of MEMS/NEMS devices using graphene process includes trench etching, wafer backside etching, graphene transfer, and mass release, which are described in a comprehensive manner. This review provides interesting perspectives for lock-in detection of weak fluorescent signals, NEMS position detection, electromechanical control of the on-chip transmitter, and single-photon-level fast electromechanical optical modulation. There are various applications of MEMS/NEMS devices, namely radio frequency devices, optic NEMS, pressure sensors, inertial sensors, which have been discussed in detail. The review mainly focusses on the devices made up of graphene (atom-layer distance of ~0.335 nm) as a main electronic/mechanical material due to its remarkable mechanical and electrical (Young’s modulus of up to ~1 TPa cm2Vs-1) and charge-carrier mobility of up to 200,000, which makes it an extremely promising membrane and transducer material for MEMS/NEMS system applications. Modern MEMS/NEMS experiments utilize mechanical resonators to push the bounds of force and mass sensing, demonstrate novel electromechanical circuit applications, measure the structural properties of materials are also covered in this review.

Fabrication of 3D metallic glass architectures by a mold-strain-set method

Metallic glasses (MGs) are considered as promising materials for microelectromechanical systems (MEMS) due to their excellent mechanical properties combined with unique net shape formability. However, the prevalent fabrication of MG MEMS is based on semiconductor micro-manufacturing technology which is limited to 2D. This work introduces a mechanically guided manufacturing method which enables facile fabrication of free-standing 3D MG structures with predictable complex and high-aspect-ratio configuration. As examples, 3D MG architectures with out-of-plane aspect ratio up to three and MG microhelices arrays are fabricated. Most critically, we show the prepared architectures exhibit super-elasticity. Such unprecedented elasticity originates from the near-ideal elastic limit of MGs, combining with geometric optimization. Finally, we demonstrate that the microstructure of the MG 3D architectures can be tuned over a wide range, which is desirable in a wide range of applications such as sensing and energy harvesting devices.

Characterization of AlScN-Based Multilayer Systems for Piezoelectric Micromachined Ultrasound Transducer (pMUT) Fabrication

Scandium-alloyed aluminum nitride (AlScN) is a potential material for micro-electromechanical systems because of its unique advantages, such as strong piezoelectric effect and high thermal stability. However, issues related to its stability and interaction with other materials in multilayer systems require investigation. The formation of new phases at the interface between piezomaterial and electrode material can lead to the device failure. In this study, multilayer structures Si substrate/AlN/Ti-Mo/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> N/top electrode (TE) were studied after annealing at a wide range of temperatures and durations. Four different TE materials (i.e. Al, AlSi (1%), Mo/Al, and Mo) were examined to determine the most reliable electrode material for the structure. The phase stability, interfacial quality, and piezoelectric response of the multilayer systems after thermal annealing were investigated. The structure with Mo TE layer was stable after annealing at 800 °C for 300 h and at 1000 °C for 100 h. None of the structures formed any new phases at the interface between the electrode layer and AlScN. The transverse piezoelectric coefficient (e <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31,f</sub> ) was determined for Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> N before and after annealing. The absolute value of the e <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31,f</sub> was -1.39 C/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for as-deposited structure and -1.67 C/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for the same structure annealed for 300 h at 800 °C. [2020-0361]

Demonstration of tantalum as a structural material for MEMS thermal actuators

This work demonstrates the processing, modeling, and characterization of nanocrystalline refractory metal tantalum (Ta) as a new structural material for microelectromechanical system (MEMS) thermal actuators (TAs). Nanocrystalline Ta films have a coefficient of thermal expansion (CTE) and Young’s modulus comparable to bulk Ta but an approximately ten times greater yield strength. The mechanical properties and grain size remain stable after annealing at temperatures as high as 1000 °C. Ta has a high melting temperature (Tm = 3017 °C) and a low resistivity (ρ = 20 µΩ cm). Compared to TAs made from the dominant MEMS material, polycrystalline silicon (polysilicon, Tm = 1414 °C, ρ = 2000 µΩ cm), Ta TAs theoretically require less than half the power input for the same force and displacement, and their temperature change is half that of polysilicon. Ta TAs operate at a voltage 16 times lower than that of other TAs, making them compatible with complementary metal oxide semiconductors (CMOS). We select α-phase Ta and etch 2.5-μm-thick sputter-deposited films with a 1 μm width while maintaining a vertical sidewall profile to ensure in-plane movement of TA legs. This is 25 times thicker than the thickest reactive-ion-etched α-Ta reported in the technical literature. Residual stress sensitivities to sputter parameters and to hydrogen incorporation are investigated and controlled. Subsequently, a V-shaped TA is fabricated and tested in air. Both conventional actuation by Joule heating and passive self-actuation are as predicted by models.

Performance analysis of bimorph cantilever beam using piezoelectric materials and MEMS technology

This research paper is an attempt to present an insight into the use of micro electromechanical systems (MEMS) technology harvesting of green energy. One of the common examples of MEMS technology is by utilizing bimorph cantilever beams. Subsequently, it has also been discussed that Bimorph cantilever beam based sensors with high sensing ability could be used for harvesting energy from the physical environment. In this paper, we concentrate on the comparative analysis of the MEMS and piezoelectric materials which are used to design bimorph cantilever beams and convert mechanical energy into electrical energy. Detailed performance analysis of bimorph cantilever beams made of different materials has been carried out through various simulation models. Design and the simulation of bimorph cantilever beam is performed using Comsol multiphysics 5.2. state of art software. Comparative analysis of Lead zirconate (PZT-4D) and Lead zirconate (PZT-7A) has been done in this research to find more suitable material for fabrication of bimorph cantilever beams. PZT-7A is found to provide better electrical output for various analysis performed.

Functional Microarray Platform with Self-Assembled Monolayers on 3C-Silicon Carbide.

Currently available bioplatforms such as microarrays and surface plasmon resonators are unable to combine high-throughput multiplexing with label-free detection. As such, emerging microelectromechanical systems (MEMS) and microplasmonics platforms offer the potential for high-resolution, high-throughput label-free sensing of biological and chemical analytes. Therefore, the search for materials capable of combining multiplexing and label-free quantitation is of great significance. Recently, interest in silicon carbide (SiC) as a suitable material in numerous biomedical applications has increased due to its well-explored chemical inertness, mechanical strength, bio- and hemocompatibility, and the presence of carbon that enables the transfer-free growth of graphene. SiC is also multifunctional as both a wide-band-gap semiconductor and an efficient low-loss plasmonics material and thus is ideal for augmenting current biotransducers in biosensors. Additionally, the cubic variant, 3C-SiC, is an extremely promising material for MEMS, being a suitable platform for the easy micromachining of microcantilevers, and as such capable of realizing the potential of real time miniaturized multiplexed assays. The generation of an appropriately functionalized and versatile organic monolayer suitable for the immobilization of biomolecules is therefore critical to explore label-free, multiplexed quantitation of biological interactions on SiC. Herein, we address the use of various silane self-assembled monolayers (SAMs) for the covalent functionalization of monocrystalline 3C-SiC films as a novel platform for the generation of functionalized microarray surfaces using high-throughput glycan arrays as the model system. We also demonstrate the ability to robotically print high throughput arrays on free-standing SiC microstructures. The implementation of a SiC-based label-free glycan array will provide a proof of principle that could be extended to the immobilization of other biomolecules in a similar SiC-based array format, thus making potentially significant advances to the way biological interactions are studied.

Analysis of the Thermoelastic Damping Effect in Electrostatically Actuated MEMS Resonators

An important aspect that must be considered when designing micro-electro-mechanical systems (MEMS) for all domains, including robotics, is the thermoelastic damping which occurs when the MEMS material is subjected to cyclic stress. This paper is focused on a model for the thermoelastic damping developed based on the generalized thermoelastic theory with the non-Fourier thermal conduction equation. The model was implemented in MATLAB and several simulations were performed. The theoretical results show a decrease in the deflection amplitude with the increase in time. The deflection amplitude decrease was validated by the experimental investigations, consisting of measuring the loss in amplitude and velocity of oscillations as a function of time. Moreover, this paper also presents the influence of the geometric dimensions on the mentioned decrease, as well as on the initial and final values of the amplitude for several polysilicon resonators investigated in this paper.

Pull-In and Snap-Through Analysis of Electrically Actuated Viscoelastic Curved Microbeam

Microbeams are key elements in most of the micro-electromechanical systems (MEMS). Electromechanical instability of microbeams in turn plays an important role in their applications. The shape and mechanical properties of microbeams dictate their functional characteristics. Focusing on their instability-based working mechanism, one can appreciate that viscoelasticity of MEMS materials cannot be neglected. Consequently, the analysis of instability in viscoelastic curved microbeams is an essential demand. In this research, assuming a clamped-clamped initially curved microbeam, the effects of viscoelastic behavior on the snap-through and pull-in instabilities are investigated. The standard inelastic linear solid model is used for the simulation of viscoelastic behavior. Integrodifferential governing equation of the curved viscoelastic microbeam is obtained by assuming modified couple stress theory and using Hamilton’s principle. By applying the Galerkin method, the obtained governing equation is discretized, converted to a nonlinear differential equation, and solved by MATLAB software. Through a quasi-static analysis, the voltage and location of snap-through and pull-in instabilities are identified. The effects of different viscoelastic parameters including the creep moduli and relaxation coefficient upon the snap-through and pull-in instabilities are investigated. The effects of different short- and long-term creeping characteristics of viscoelastic microbeam are studied and discussed in detail.

In Situ XRD Observation of Crystal Deformation of Piezoelectric (K,Na)NbO3 Thin Films

(K,Na)NbO3 (KNN) thin films are promising lead-free piezoelectric materials for microelectromechanical systems (MEMS) devices. However, the origin of the strong piezoelectric properties of KNN thin...

Fracture strength and fatigue endurance in Gd-doped ceria thermal actuators

We studied the stability of the mechanical properties and the fatigue endurance of Gd-doped ceria (CGO), which is a promising electromechanically active material for microelectromechanical systems (MEMS). Specifically, the fracture strength and long-term operation of plate-type circular (2 mm diameter) thermal actuators made of ≈1.15 μm thick Ce0.95Gd0.05O1.975 (CGO5) were investigated. Excitation voltage of 10 V at the frequency range between 1 and 2.1 MHz induces Joule heating effect that can generate an in-plane strain of ≈0.1 %. The operation temperature ranged from 25 °C to 80 °C and the temperature shift, caused by the AC heating, was about 80 K at 10 V. Critical fracture was found to occur at out-of-plane displacements between ∼35 and ∼42 μm, which corresponds to the average bending stress of ∼44 MPa at the center of the plate. During long-term operation, the actuators exhibit gradual decrease in the response, probably due to contact degradation. However, structural damage or mechanical fatigue was not found even after 107 cycles at a stress level of ∼30 % of the critical fracture strength.

SiC nanowire-based SU-8 with enhanced mechanical properties for MEMS structural layer design

In addition to being used for pattern transfer, the negative photoresist SU-8 is widely used as a structural material in microelectromechanical systems (MEMS). Due to its good photopatternability, SU-8 has lower manufacturing costs than many other materials, but its mechanical properties are relatively weak to some extent, which limits its performance. The mechanical properties of epoxy-like SU-8 can be enhanced by adding micro- or nano-fillers such as carbon nanotube, clay, and SiC nanowire, which have superior elastic modulus. In this study, SiC nanowires were used to improve the mechanical properties of SU-8 while the SU-8 retains its photopatternability. The SiC nanowires were uniformly dispersed in SU-8 by stirring and ultrasonication. SU-8 materials with different SiC nanowire contents were fabricated into dog bone samples by lithography. The elastic modulus, storage modulus, and damping factor of the samples were measured by the Dynamic mechanical analysis (DMA) Q800. The experiment result shows that the rigidity and toughness increased, and the damping reduced. The 2 wt% SiC nanowires-reinforced SU-8 had a 73.88% increase in elastic modulus and a 103.4% increase in elongation at break. Furthermore, a spring component made by SiC-doped SU-8 could withstand greater acceleration. The SiC nanowires-reinforced SU-8 has the potential to meet higher requirements in the design and manufacture of MEMS and greatly reduce the manufacturing costs of MEMS devices.

Investigation of graphene as a material for electrical contacts in the application of microrelays using finite element modeling

This paper investigates the use of Graphene (Gr) as an electrical contact material for the application of microrelays. Gr is an ideal material for microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS). A microrelay has been considered and electrothermal analysis is carried out based on Finite Element Modeling (FEM) using COMSOL Multiphysics simulation tool. Electrical contact surfaces for the material Al, Cu, Ag and Gr have been analyzed. The electrical contact resistance, voltage drop, current density, resistive losses and temperature of the contact interface has been obtained. The results obtained have been verified using theoretical calculations. Also, the combustion voltage of Gr electrical contact has been obtained as 0.2 V at which the Gr reaches its combustion temperature of 623 K. The results show that Gr electrical contact performs better in terms of electrical and thermal performance parameters which would be used in future electrical components.

Micro-ultrasonic drilling of monocrystalline silicon: An experimental investigation on machined surface topography and optimization using User's preference rating based TOPSIS

In the current scenario, silicon is extensively used as raw material in microelectromechanical systems and microelectronic devices. But, it has low fracture toughness that renders it difficult to process by conventional machining techniques. Thus, to overcome the barriers of conventional machining, rotary tool micro-ultrasonic drilling (RT-MUSD) process has been attempted for machining of silicon in this research endeavour. Taguchi's L9 orthogonal array was adopted as experimental design. The influence of variable parameters viz. rotation speed, power rating and abrasive size were analysed on performance characteristics (i.e. hole overcut (HOC), taper angle (TA) and material removal rate (MRR)) of RT-MUSD process. Analysis of variance (ANOVA) was applied to determine the significant parameters affecting the RT-MUSD process. Subsequently, optimal parametric setting for minimum HOC and TA and maximum MRR was obtained through user's preference rating based technique for order preference by similarity to ideal solution method. The ANOVA results showed that rotation speed was the most influencing parameter affecting the HOC, TA and MRR. The optimal parametric combination resulted in an average improvement of 26% in the performance of RT-MUSD process. The machined surface topography revealed that two types of material removal mode (i.e. pure brittle fracture and ductile + brittle fracture) occurred during RT-MUSD of silicon.