Sacrificial Layer Process Research Articles

Epitaxial ZnO piezoelectric layer on SiO2/Mo solidly mounted resonator fabricated using epitaxial Au sacrificial layer

In solidly mounted resonator (SMR) type of bulk acoustic wave resonator, it is difficult to fabricate single crystalline piezoelectric thin films in a bottom-up process due to the amorphous SiO2 in the low acoustic impedance layer of the acoustic Bragg reflector. In this study, single crystalline ZnO piezoelectric layer on amorphous SiO2/polycrystalline Mo acoustic Bragg reflector is fabricated using a wet etching process of the epitaxial Au sacrificial layer. Epitaxial growth of ZnO was confirmed by X-ray diffraction pole figure and transmission electron microscope electron diffraction pattern. Resonance frequency of 1.3 GHz of epitaxial ZnO SMR was observed using a network analyzer.

Improving consistency and performance of graphene-based devices via Al sacrificial layer

Graphene has attracted much attention because of its excellent physical properties and great potential applications in electronic devices. However, traditional lithography process using photoresist masks will inevitably leave some organic matter on the graphene surface, which will reduce the performance and yield of graphene-based devices. In this paper, a new lithography process for the separation of graphene and photoresist using Al sacrificial layer is proposed. ToF-SIMS demonstrated that the process not only avoids photoresist residues, but also significantly reduces PMMA contamination without introducing Al atomic residues. The morphology also shows that the graphene pattern prepared by this process is flatter and cleaner. More importantly, electrical tests show that Al sacrificial layer process can significantly improve the consistency of the resistance (standard deviation reduced by 41.9%) and the sensitivity of the device (temperature sensor sensitivity increased by 54.41%). This work provides a way for the commercial application of graphene electronic devices.

A High-Reliability RF MEMS Metal-Contact Switch Based on Al-Sc Alloy.

This paper presents a new metal-contact RF MEMS switch based on an Al-Sc alloy. The use of an Al-Sc alloy is intended to replace the traditional Au-Au contact, which can greatly improve the hardness of the contact, and thus improve the reliability of the switch. The multi-layer stack structure is adopted to achieve the low switch line resistance and hard contact surface. The polyimide sacrificial layer process is developed and optimized, and the RF switches are fabricated and tested for pull-in voltage, S-parameters, and switching time. The switch shows high isolation of more than 24 dB and a low insertion loss of less than 0.9 dB in the frequency range of 0.1-6 GHz.

Use of 3d printing technology in the treatment of microtia and other outer ear deformities

Introduction: Microtia and other outer ear deformations may cause a lot of psychical, social, and mental stress for a patient. In order to surgically treat it, we need a very experienced plastic surgeon specializing in such operations. With the use of 3D printing technology, such as fused deposition modeling or a sacrificial layer process there are a lot of possibilities starting from creating aids for plastic surgeons to printing ear prosthesis from live cells. Objective: The study's objective was to research, review and compare data available on PubMed about the use of 3D printing in the treatment of microtia and other ear deformations. A brief description of the state of knowledge: With the current state of knowledge, with the 3D printing technology, we can quickly create highly individualized and helpful training aids for plastic surgeons that would help them during operations. There is also a possibility of developing a personalized splint that would help correct the ears better than conventional methods. What’s more, we can also print prosthetics, not only with the use of conventional materials used in 3D printing but also with live chondrocytes and adipocytes that were able to chondro and adipogenesis, respectively. Conclusions: There are a couple of ways we can use 3D printing in the treatment of outer ear deformities. The most promising is printing with live cells, but we need more research to develop better methods and techniques to use in the future prosthetics.

Pressure-Sensitive Nano-Sheet for Optical Pressure Measurement.

Pressure-Sensitive Paint (PSP) is a powerful measurement technique to obtain pressure distribution on a model of interest by measuring the emission intensity of the PSP coating with a camera. Since a PSP coating is prepared by applying a solution containing an organic solvent, generally, by sprayer, the properties such as the pressure- and the temperature-sensitivity depends on the skill of the person applying it. This fabrication process is one of the barriers to use of the PSP technique because of the legal restrictions on the use of organic solvents. Thus, a sticker-like PSP coating is useful because it does not require the use of organic solvent and the applying skill. In this study, we have fabricated freestanding Pressure-Sensitive Nano-Sheet (PSNS) by a sacrificial layer process using a spin-coating method. We employed Pt(II) meso-tetra(pentafluorophenyl)porphine (PtTFPP) as a pressure-sensitive dye and poly(1-trimethylsilyl-propyne) (PTMSP) and poly(L-lactic acid) (PLLA) as a polymer binder; thus, the PSNS samples based on PTMSP and PLLA were prepared. The pressure- and the temperature-sensitivity, the lifetime of the luminescence, and the quantum yield of the fabricated PSNS have been investigated. The pressure-sensitivity of PTMSP-based PSNS is higher than that of PLLA-based PSNS. Conversely, the quantum yield of PLLA-based PSNS is higher than that of PTMSP-based PSNS.

Sub-10-nm-thick SiN nanopore membranes fabricated using the SiO2 sacrificial layer process

In our previous studies, ultrathin SiN membranes down to 3 nm in thickness were fabricated using the poly-Si sacrificial layer process, and nanopores were formed in those membranes. The region of the SiN membrane fabricated using this process was small, and the poly-Si sacrificial layer remained throughout the other region. On the other hand, to reduce the noise of the current through the nanopore, it is preferable to reduce the capacitance of the nanopore chip by replacing the poly-Si layer with an insulator with low permittivity, such as SiO2. Thus, in this study, the fabrication of SiN membranes with thicknesses of 3–7 nm using the SiO2 sacrificial layer process was examined. SiN membranes with thicknesses of less than 5 nm could not be formed when the thickness of the top SiN layer deposited onto the sacrificial layer was 100 nm. In contrast, SiN membranes down to 3.07 nm in thickness could be formed when the top SiN layer was 40 nm in thickness. This is thought to be due to the difference in membrane stress. Nanopores were then fabricated in the membranes via dielectric breakdown. The current noise of the nanopore membranes was approximately 3/5 that of membranes fabricated using the poly-Si sacrificial layer process. Last, ionic current blockades were measured when poly(dT)60 passed through the nanopores, and the effective thickness of the nanopores was estimated based on those current-blockade values. The effective thickness was approximately 4.8 nm when the deposited thickness of the SiN membrane was 6.03 nm. On the other hand, the effective thickness and the deposited thickness were almost the same when the deposited thickness was 3.07 nm. This suggests it became difficult to form a shape in which the thickness of the nanopore edge was thinner than the deposited membrane thickness as the deposited thickness decreased.

Mass Transfer of Microscale Light-Emitting Diodes to Unusual Substrates by Spontaneously Formed Vertical Tethers During Chemical Lift-Off

A much simplified method for transferring Gallium nitride (GaN) light emitting didoes (LEDs) to an unusual substrate, such as glass, Si, polyethylene terephthalate, or polyurethane, was demonstrated with spontaneously formed vertical tethers during chemical lift-off (CLO), without requiring a sacrificial layer or extra process steps. The LED arrays resided on a stamp that was coated with an adhesive layer. After the layer with the LEDs was transferred to the new substrates, the stamp was removed by acetone to complete the preparation. Over 3 × 3 cm2 LED arrays transferred to various substrates without any damage and misorientation. We also found that the optical and electrical characteristics improved after transfer due to decease in built-in stress. This simple and practical method is expected to greatly facilitate the development of transferrable full color GaN microLEDs on various substrates with either greatly reduced or no damage.

Structurally isolated photoactuation of graphene-mixed temperature-responsive hydrogels in soft-rigid series structure

This paper presents fabrication and actuation methods for a soft microrobot with a hybrid structure composed of soft microactuators and a rigid supporting body. This hybrid structure enables actuation of the microrobot with independent driving of multiple actuators to provide complex movement like that of living microorganisms. We use the temperature-responsive hydrogel poly(N-isopropylacrylamide) (PNIPAAm) as a soft microactuator. PNIPAAm swells with water at low temperature but shrinks at high temperature. This volume change thus allows PNIPAAm to be used as an actuator by controlling its temperature. We successfully fabricated the microrobot with its soft-rigid hybrid structure composed of PNIPAAm and rigid photoresist using a multilayered microfabrication process. In addition, we used a sacrificial layer process to release the fabricated microrobot from the substrate to allow it to move freely. To actuate the microrobot, we mixed PNIPAAm with graphene, which has a high photothermal conversion efficiency. The temperature of the soft actuator when mixed with graphene can be increased by irradiating it with light. Therefore, actuation of the microrobot is achieved by sequentially irradiating the microactuators with focused light. We present the fabrication, release and partial actuation of the microrobot to demonstrate the feasibility of the proposed microrobot with the soft-rigid hybrid structure in this paper.

PMMA-Based Wafer-Bonded Capacitive Micromachined Ultrasonic Transducer for Underwater Applications.

This article presents a new wafer-bonding fabrication technique for Capacitive Micromachined Ultrasonic Transducers (CMUTs) using polymethyl methacrylate (PMMA). The PMMA-based single-mask and single-dry-etch step-bonding device is much simpler, and reduces process steps and cost as compared to other wafer-bonding methods and sacrificial-layer processes. A low-temperature (<) bonding process was carried out in a purpose-built bonding tool to minimize the involvement of expensive laboratory equipment. A single-element CMUT comprising 16 cells of 2.5 radius and 800 cavity was fabricated. The center frequency of the device was set to 200 kHz for underwater communication purposes. Characterization of the device was carried out in immersion, and results were subsequently validated with data from Finite Element Analysis (FEA). Results show the feasibility of the fabricated CMUTs as receivers for underwater applications.

Fabricating freely suspended structures optimized regarding mechanical and electrochemical stability for sensor applications

The concept of the micro-structured gas sensor discussed in this article promises the measurement of gas concentration and identification of gaseous substances in-situ. Furthermore it is fabricated exclusively using processes that are part of standard CMOS technology. In most MEMS devices a suspended structure is the main part of the sensor chip, realised using a wet etching sacrificial layer process. In this research we investigated the mechanical stability of different materials for the levitating structure and the electrochemical compatibility of the materials in the chip. A detailed analysis of the reactions of different material combinations in buffered oxide etch (BOE) revealed the occurrence of corrosion and hydrogen embrittlement in Al-ITO-LaB6 systems. From there a new mechanism of hydrogen embrittlement in thin film layer systems with ITO was proposed. Finally we showed an optimized way of fabricating the sensor chip with prevention of corrosion and hydrogen embrittlement by galvanic isolation.

An advanced tunnel oxide layer process for 65 nm NOR floating-gate flash memories

An advanced tunnel oxide layer process for 65 nm NOR-type floating-gate flash memory is proposed to improve tunnel oxide quality by an additive sacrificial oxide layer growth. The sacrificial oxide layer process effectively controls the thickness variation of tunnel oxide and improves the flatness of the SiO2/Si interface across the active area. The interface traps’ generation during program/erase cycling of flash cells is found to be reduced, and the reliability property is significantly improved as compared to flash cells without the sacrificial oxide layer process. The technology is applicable to further scaled floating-gate flash memories.

Selective patterning of indium tin oxide films using 1064 nm laser for microparts processing

Conventional metal microparts were fabricated by a series of complex photolithography, sputtering, sacrificial layer and release processes. This reported work demonstrates the integrated process of metal microparts using 1064 nm Nd:YVO4 laser direct-write patterning of indium tin oxide (ITO) thin films on glass, followed by the electrochemical deposition of copper (Cu) on the pattern. The ITO thin film could be removed without any damage to the glass structure through the diffractive multiple Nd:YVO4 beam. A high overlapping area of the laser spot was used to pattern the electrode layer on the film surface for obtaining a 50 µm ablated edge profile with a linear boundary after laser patterning. A high quality of surface could be achieved at a proper parameter control without numerous processing steps. Compared with conventional photolithography and etching technologies, direct-write micropatterns of ITO using the Nd:YVO4 laser is a maskless, dry and low-cost process. Accordingly, the micrometal parts can be obtained using the electrochemical deposition and release process of laser-patterned ITO films because of the adhesion property of Cu on ITO.

Fabrication of novel MEMS inertial switch with six layers on a metal substrate

MEMS inertial switches have great potential to be widely used in toys, accessories, automotive, military weapons and industrial applications in recent years. Combining with UV-LIGA technology, a new fabrication method of multilayer movable microstructures on metal substrates is presented in this paper, by which a kind of MEMS omnidirectional inertial switch with six layers has been fabricated on metal substrate directly. The method consists of double alignment marks etching process on the back of metal substrates, SU-8 thick photoresist with high aspect ratio lithography process, micro electroforming process, no back plate growing process and SU-8 photoresist sacrificial layer process. Some problems in the fabrication process, such as poor adhesion property among electroforming deposit layers, high stress in electroforming layers, difficulty of preparing the SU-8 mould with high aspect ratio, have been solved effectively. The smallest dimension of the switch is 15 μm, the highest aspect ratio achieves 6:1, the total height of the switch is 210 μm and the outline size is 2.8 × 2.8 mm. The fabrication method presented in this paper provides a new option for the development of multi-layers micro metal devices and is helpful for the fabrication of similar kinds of micro devices.

Segmented magnetic circuit simulation of the large displacement planar micro-coil actuator with enclosed magnetic yokes

This paper proposed the segmented magnetic circuit method to simulate the large displacement planar micro-coil (PMC) microactuator for micro-magnetic relay applications, which adopted enclosed miniaturized magnetic yokes. The segmented magnetic circuit model has been established to describe the magnetic flux variation and the redistribution effects of the magneto motive force (MMF) induced by the large air gap and large ratio between the radical and vertical size. Based on the optimized parameters, the PMC microactuator was fabricated through UV-LIGA technology and tested to verify the model under scrutiny. The large displacement was realized by using laminated photoresist sacrificial layer process. After comparing the measurement and simulation results, it is concluded that the modified model can describe the influence of key parameters over the output electromagnetic force. The proposed methodology is demonstrated to be efficient in the analysis and optimization of the magnetic MEMS devices of PMC structures with embedded magnetic yoke.

A laterally-driven micromachined inertial switch with a compliant cantilever beam as the stationary electrode for prolonging contact time

A novel micro-electromechanical systems inertial switch based on non-silicon surface micromachining technology has been designed, fabricated and characterized in the present work. Compared with the traditional inertial switch, a compliant cantilever beam as a stationary electrode has been proposed to prolong the contact time, which can realize sufficient elastic deformation during the contact between the electrodes. The dynamic contact process is analyzed theoretically and the corresponding mechanical impact mechanism is also explained. To investigate the contact-enhancing mechanism of the cantilever beam, the switch applied half-sine acceleration with various amplitudes in the sensitive direction is simulated with ANSYS software. The dynamic simulation results confirm the contact-enhancing mechanism described by the theoretical analysis and it is shown that the contact time (i.e., the switch-on time) can be prolonged effectively by utilizing the elastic deformation of the cantilever beam and increased with the applied accelerations. The inertial switch is successfully fabricated by electroplating and sacrificial layer processes technologies. The prototype has been characterized by dropping hammer experiment. The test results indicate that the contact effect is improved significantly and the contact time is ∼80 µs under the 297 g acceleration, and the maximum value is ∼410 µs for the 672 g acceleration amplitude, which is in general accordance with the simulated results. The mechanical contact between the cantilever beam and the proof mass is evaluated following thousands of impacts. The scanning electron micrographs of the contact surfaces indicate that the all-metal switch still keeps a good mechanical property after suffering the hot contact, and the contact resistance is also stable.

3D printing of composite tissue with complex shape applied to ear regeneration

In the ear reconstruction field, tissue engineering enabling the regeneration of the ear's own tissue has been considered to be a promising technology. However, the ear is known to be difficult to regenerate using traditional methods due to its complex shape and composition. In this study, we used three-dimensional (3D) printing technology including a sacrificial layer process to regenerate both the auricular cartilage and fat tissue. The main part was printed with poly-caprolactone (PCL) and cell-laden hydrogel. At the same time, poly-ethylene-glycol (PEG) was also deposited as a sacrificial layer to support the main structure. After complete fabrication, PEG can be easily removed in aqueous solutions, and the procedure for removing PEG has no effect on the cell viability. For fabricating composite tissue, chondrocytes and adipocytes differentiated from adipose-derived stromal cells were encapsulated in hydrogel to dispense into the cartilage and fat regions, respectively, of ear-shaped structures. Finally, we fabricated the composite structure for feasibility testing, satisfying expectations for both the geometry and anatomy of the native ear. We also carried out in vitro assays for evaluating the chondrogenesis and adipogenesis of the cell-printed structure. As a result, the possibility of ear regeneration using 3D printing technology which allowed tissue formation from the separately printed chondrocytes and adipocytes was demonstrated.

Preparation of sacrificial layer for MEMS devices by lift-off technology

To simplify the preparation of sacrificial layer in micro-electromechanical system structure, new processes have been developed. By using lift-off technology, sacrificial layer was selectively deposited into the pit that prepared for sacrificial layer releasing. Then a short time polishing process was used to remove the burrs around the pit. This method offers several advantages including reducing the difficulty of polishing and hence processing cost. Methods and apparatuses to provide a continuously smoothly sacrificial layer surface in the pit were disclosed. However, it is important to control the homogeneity of filling and avoid the shadow effect at the corner of the pit. The unpadded regions would form a steep step and cause the cracking of structure layer. This problem was discussed and solved by rotating the tilted wafer during sacrificial material deposition. The surface roughness after the preparation process of sacrificial layer was measured. The root mean square roughness of sacrificial layer was 1.247 nm and reduced to 0.861 nm after a short time polishing process. Finally, a film bulk acoustic wave resonator with stacked Mo/AlN/Mo films had been fabricated on the sacrificial layer based on this method.

Nanofabrication, effects and sensors based on micro-electro-mechanical systems technology

In this paper, our investigation of nanofabrication, effects and sensors based on the traditional micro-electro-mechanical systems (MEMS) technology has been reviewed. Thanks to high selectivity in anisotropic etching and sacrificial layer processes, nanostructures such as nanobeams and nanowires have been fabricated in top-down batch process, in which beams with thickness of only 20 nm and nanowires whose width and thickness is only 20 nm were achieved. With the help of MEMS chip, the scale effect of Young's modulus in silicon has been studied and confirmed directly in a tensile experiment using electron microscopy. Because of their high surface-to-volume ratio and small size, silicon nanowire (SiNW)-based field-effect transistors (FETs) have been shown as one of the most promising electronic devices and ultrasensitive detectors in biological applications. We demonstrated that an SiNW-FET sensor can reveal ultrahigh sensitivity for rapid and reliable detection of 0.1 fM of target DNA with high specificity. All these indicate that the MEMS technology can pave the way to nanoapplications with its advantages of batch production, low cost and high performance.

3D printing of cell-laden constructs for heterogeneous tissue regeneration

Abstract Three-dimensional (3D) printing of relevant components of tissue, such as cells and matrix material, has been used for fabrication of tissue analogs. However, fabrication using existing cell printing systems is difficult for printing of tissues with complex shapes and compositions. In this study, we successfully printed 3D cell-laden constructs using the principle of hybrid structure fabrication. A sacrificial layer process, in combination with current 3D printing technology, was used to fabricate complex shaped tissues. We demonstrated practicality of using 3D printing to fabricate cell-laden constructs, where cells were localized as intended. The cell viability of the fabricated constructs was high.

Screen printing of a capacitive cantilever-based motion sensor on fabric using a novel sacrificial layer process for smart fabric applications

Free-standing cantilevers have been fabricated by screen printing sacrificial and structural layers onto a standard polyester cotton fabric. By printing additional conductive layers, a complete capacitive motion sensor on fabric using only screen printing has been fabricated. This type of free-standing structure cannot currently be fabricated using conventional fabric manufacturing processes. In addition, compared to conventional smart fabric fabrication processes (e.g. weaving and knitting), screen printing offers the advantages of geometric design flexibility and the ability to simultaneously print multiple devices of the same or different designs. Furthermore, a range of active inks exists from the printed electronics industry which can potentially be applied to create many types of smart fabric. Four cantilevers with different lengths have been printed on fabric using a five-layer structure with a sacrificial material underneath the cantilever. The sacrificial layer is subsequently removed at 160 °C for 30 min to achieve a freestanding cantilever above the fabric. Two silver electrodes, one on top of the cantilever and the other on top of the fabric, are used to capacitively detect the movement of the cantilever. In this way, an entirely printed motion sensor is produced on a standard fabric. The motion sensor was initially tested on an electromechanical shaker rig at a low frequency range to examine the linearity and the sensitivity of each design. Then, these sensors were individually attached to a moving human forearm to evaluate more representative results. A commercial accelerometer (Microstrain G-link) was mounted alongside for comparison. The printed sensors have a similar motion response to the commercial accelerometer, demonstrating the potential of a printed smart fabric motion sensor for use in intelligent clothing applications.