This PDF file contains the editorial “Impacts of electronic publication” for JM3 Vol. 8 Issue 02

This PDF file contains the editorial “Guest Editorial: Theory and Practice of MEMS/NEMS/MOEMS, RF MEMS, and BioMEMS” for JM3 Vol. 8 Issue 02

We reports a detailed study on a novel design of a Joule-heating-induced polymerase chain reaction (PCR) microchip directly heated by applying electric current to the ends of the geometric varied microchannel, which is simulated together with the factors acting on the temperature distribution. Treating the continuous flowing fluid in the channel as the resistance, different channel shapes would lead to the different resistances, which generates various heat when the fixed current is applied to the ends of channel. Based on the Ohm's law and the Joule-Thomson effect, three required sequential temperature zones are obtained. The temperature cycling is achieved and the factors that contribute to the temperature distribution are simulated and analyzed, such as the environment temperature, the heat transfer coefficient, the current density, the fluid velocity, and the channel shape. The design of the Joule-heating-induced PCR microchip sheds light on the future novel application of continuous-flow PCR. By applying certain conditions, thermal cycles that meet PCR requirements can be achieved.

We present the fabrication and optimization of new integrated microgiant electrorheological (GER) valves for microflow cytometry. Compared to previous GER valves, new GER valves, consisting of an SU-8 layer, a PDMS membrane, and glass layers, were fabricated by 4-mask microelectromechanical systems technology and two new packaging methods. This design enabled good bonding and fluidic interconnection. The thickness of the PDMS membrane was designed such that the membrane deformation was large enough that the cytometry channel was well sealed. The interfacial stress between the PDMS and the PDMS/SU-8 as a function of vacuum plasma treatment time was investigated in detail. The switching behavior of the GER valves was also analyzed and characterized using fluorescence microscopy.

In an effort to develop a novel electronic paper image display technology based on the electrowetting principle, a 3-D electrowetting cell is designed and fabricated, which consists of two 3-D bent electrodes, each having a horizontal surface made of gold and a vertical surface made of indium tin oxide (ITO) glass as a color display window, a layer of dielectric material on the 3-D electrodes, and a highly fluorinated hydrophobic layer on the surface of the dielectric layer. Results of this work show that an electrowetting-induced motion of an aqueous droplet in immiscible oils can be achieved reversibly across the boundary of the horizontal and vertical surfaces of the 3-D electrode surface. It is also shown that the droplet can maintain its wetting state on a vertical sidewall electrode free of a power supplier when the voltage is removed. This phenomenon may form the basis for color contrast modulation applications, where a power-free image display is required, such as electronic paper display technology in the future.

We report a novel passive microfluidic mixer design for mixing enhancement based on dynamic disturbances due to bubble generation produced by catalytic decomposition of hydrogen peroxide. A Y-shaped passive microfluidic mixer with a width and depth of 1 mm and 50 µm, respectively, with platinum deposition on the partial undersurface of the mixing channel for H₂O₂ catalytic decomposition, is demonstrated. Various Reynolds numbers (0.06 to 63.5) and H₂O₂ concentrations are tested to investigate their effects on the mixing. The experimental results show that mixing can be significantly improved either with the decrease of volumetric flow rate at a given H₂O₂ concentration or with the increase of H₂O₂ concentration at intermediate Reynolds numbers based on the present design. The mixing index scatters between 0.8 and 1.0 at x ≥ 15 mm for all H₂O₂ concentrations if Re=0.06 in the mixing channel. However, the H2O2 concentration has no significant effect on mixing provided Re ≥ 63.5. In addition, the maximum mixing enhancement for Q_L=1, 10, 100, and 1000 µL/min (Re=0.06, 0.63, 6.35, and 63.5) at x ≥ 15 mm are 5.7, 11.85, 6.27, and 4.8, respectively, with 0.1 M<[H₂O₂]<8.8 M in this study.

We study particle levitation in a dielectrophoretic field-flow fraction (DEP-FFF) flow sorter by using theoretical and numerical methods. By balancing DEP forces with gravitational and buoyant forces, one can obtain the analytical solution for the particle levitation height. Numerical simulation is carried out and used to compare with the analytical prediction. One can find that there exists a maximum particle levitation height at a specific electrode width (d) for each applied voltage. The maximum levitation height happens at h_p/d=0.95. The particle behaviors can be discussed based on the ratio between levitation height (h_p) and the width of electrode (d). When levitation height is higher than h_p/d<0.6, simulation results show excellent agreement (less than 2% error) with the first-order approximated analytical solution. When levitation height is between 0.43<h_p/d<0.6, the results start to show the large discrepancies (more than 2% error) between simulation and the first-order approximated analytical solution. A higher order theoretical solution has to be considered for this situation. When levitation height is h_p/d<0.43, particles will stick on the bottom wall. Approximate theoretical solution is no longer applicable.

Electrokinetics provide an effective molecular manipulation technique in micro/nano fluidic environments, which match the length scale of various biological objects. In this work, two circular gold electrodes are fabricated on a glass substrate as DNA concentrators. A combination of alternating current (ac) electro-osmosis and electrophoresis is used to concentrate single-stranded DNA (ssDNA) molecules as small as 20 nucleotides in length. To understand the phenomenon of ac electro-osmotic flow, numerical simulation of the flow field is done and shows that the effective fluid flow is up to 100 µm above the electrode surface. Hence, ssDNA molecules labeled with fluorescent dye are utilized to demonstrate the concentration effect on the DNA concentrator. ac electro-osmotic flow induced by the ac electric field can stir the bulk fluid, and ssDNA molecules can be transported from a large effective region to the surface of DNA concentrator. In addition, electrophoretic force induced by direct current (dc) bias is applied simultaneously to attract and hold ssDNA molecules. The motion of ssDNA molecules under electrokinetic forces is observed under a fluorescence microscope. The experimental results show that the ssDNA molecules can be concentrated on the electrode surface instantly. ssDNA concentration under different conditions is also compared and the results generated are discussed.

An investigation of a VO₂ etch mechanism in Cl₂/Ar inductively coupled plasma under the condition of low ion bombardment energy is carried out. It is found that an increase in Ar mixing ratio results a nonmonotonic VO₂ etch rate, which reaches a maximum of 70 to 80 nm/min at 70 to 75% Ar. The model-based analysis of the etch mechanism shows that the VO₂ etch kinetics correspond to the ion-flux-limited etch regime. This is most likely due to the domination of low volatile VCl₃ and/or VCl₂ in the reaction products.

The deep nickel metal deposition on multiscale features with a single small hole and large sector cavities with depth of 1 mm has been investigated using direct current (DC) and pulse alternating current (AC) electroforming. The diameter of the hole is around 240 µm, and the size of the sector cavity is several mm to cm corresponding to the various aspect ratios from 0.07 to 4.17. The successful metal electroforming into both the hole and cavity features can be obtained by the AC mode, while the DC mode leads to metal electroforming only in sector cavities rather than in the small hole. This is because the surface concentration of the cathode in pulse electroforming is higher than that in DC electroforming, allowing large cations to diffuse into different multiscale features at lower overpotential. The increment factor, i.e., percentage increase in concentration used as an index of the varied surface concentration increases from 0.903 (10⁻²%) at 1 Hz to 1.077 (10⁻²%) at 100 Hz. This achievement can be used for the high aspect ratio metal electroforming of a single hole as a micro-sensing tip in different applications.

A novel single-chip microelectromechanical systems (MEMS) capacitive microphone with a slotted diaphragm for sound sensing is developed to minimize the microphone size and improve the sensitivity by decreasing the mechanical stiffness of the diaphragm. According to the results, a clamped microphone with a 2.43×2.43-mm² diaphragm and a slotted one with a 1.5-×1.5-mm² diaphragm have the same mechanical sensitivity, but the size of slotted microphone is at least 1.62 times smaller than clamped structure. The results also yield a sensitivity of 5.33×10⁻⁶ pF/Pa for the clamped and 3.87×10⁻⁵ pF/Pa for the slotted microphone with a 0.5×0.5-mm² diaphragm. The sensitivity of the slotted diaphragm is increased 7.27 times. The calculated pull-in voltage of the clamped microphone is 214 V, the measured pull-in voltage of the slotted one is 120 V. The pull-in voltage of the slotted microphone is about 50% decreased.

Polymethyl methacrylate (PMMA) microstructures were fabricated by a polymeric microreplication technology using ultrasonic vibration energy. A commercial ultrasonic welder system was used to apply ultrasonic vibration energy for micromolding. Two different types of nickel micromolds, which were equipped with pillar-type and pore-type microstructures, were fabricated. PMMA was used as the polymer microreplication material, and the optimal molding times were determined to be 2 s and 2.5 s for the pillar-type and pore-type micromolds, respectively. Compared with conventional polymer microreplication technologies, the proposed ultrasonic microreplication technology showed an extremely short processing time. Heat energy generated by ultrasonic vibration locally affected the vicinity of the contact area between the micromold and the polymer substrate. Consequently, only that very limited area was melted so that the bulk material was not seriously affected by the thermal effect and thermal shrinkage could be minimized. Furthermore, although the replication process was not performed in vacuum conditions, the ultrasonic micromolding showed high fidelity in polymer microreplication using the pore-type micromold.

We report on a novel low-power, large-displacement, vertical electrothermal actuator made of multiple materials, primarily silicon nitride, polysilicon, and nickel. The architecture of separated metal and nitride layers bypasses the limitation imposed by conventional bimorph actuators. A vertical tip displacement of 20 µm can be achieved at a driving current as low as 1.06 mA. The corresponding power consumption is 16.29 mW. Devices with different combinations of parameter values are characterized and compared. At the end of the work, we compare our device with several selections from the archives.

A novel thermoelectric cooling/heating device was proposed and fabricated as an alternative to the conventional π-type device. The novel device is the first since the conventional π-type structure was fabricated a half-century ago. The structure includes a sharp tip that is positioned between p- and n-type Bi₂Te₃ bulks, and the tip can easily be exchanged when different targets are cooled or heated. The tip sizes are 50-100 µm when a copper tip is used and 100 nm when a cantilever is used. The tip temperature reached −36.3 °C during cooling and 251.5 °C during heating. Our device is useful not only for cooling/heating micro-objects but also for heat manipulation of micro-organisms.

We present the fabrication and testing of a silicon carbide balanced mass double-ended tuning fork that survives harsh environments without compromising the device strain sensitivity and resolution bandwidth. The device features a material stack that survives corrosive environments and enables high-temperature operation. To perform high-temperature testing, a specialized setup was constructed that allows the tuning fork to be characterized using traditional silicon electronics. The tuning fork has been operated at 600°C in the presence of dry steam for short durations. This tuning fork has also been tested to 64,000 G using a hard-launch, soft-catch shock implemented with a light gas gun. However, the device still has a strain sensitivity of 66 Hz/µε and strain resolution of 0.045 µε in a 10-kHz bandwidth. As such, this balanced-mass double-ended tuning fork can be used to create a variety of different sensors including strain gauges, accelerometers, gyroscopes, and pressure transducers. Given the adaptable fabrication process flow, this device could be useful to microelectromechanical systems (MEMS) designers creating sensors for a variety of different applications.

We propose a novel fabrication process for twin probes of an atomic force microscope (AFM) that consist of a silicon dual tip with a narrow gap. The dual tip with a tetrahedral shape consists of an inclined silicon (111) plane and two vertical planes and was successfully fabricated by using the proposed fabrication process of combining deep reactive ion etching (D-RIE) for silicon trench formation along the silicon (001) direction, selective oxidation of the sidewalls of the trench, and crystalline anisotropic etching. The silicon tips could be sharpened by a low-temperature oxidation process, resulting in a tip radius of about 10 nm. In addition, the dual silicon tip formation, dual AFM probe with cantilever, and thermal actuator were also successfully fabricated from a silicon-on-insulator (SOI) water. The gap of the dual tip was about 2.9 µm, with trench etching 1 µm wide and sidewall oxidation 1 µm thick.

We present a new method for stress-free microelectromechanical systems (MEMS) flip-chip packaging. Residual stress, which is mainly generated during the reflow process, is a notorious problem in flip-chip packaging. The residual stress reduces the bump fatigue life and device performance owing to the deformation. Underfill encapsulation is a common way to reduce the residual stress in a flip-chip integrated circuit (IC) packaging process. However, it cannot be applied to MEMS packaging because MEMS devices usually include moving microstructures. We intend to resolve this problem by improving the MEMS structure, designing spring beams to introduce electrical pads. The residual stress, which is caused by the mismatch of the coefficient of thermal expansion (CTE) between the MEMS device and the package substrate, can be absorbed through the deflection of spring beams. By using this idea, a quartz MEMS-based capacitive tilt sensor, which was bulk etched and composed of vertical comb electrodes in wafer thickness for achieving large initial capacitance, was successfully packaged. A high melting point alloy Au80Sn20 was used as the solder joint material. The thermal cycling test and sensitivity evaluation experimental results demonstrated the effectiveness of the proposed method.

This work presents a power-efficient wireless sensor implemented using microelectromechanical system (MEMS)-based dry electrodes (MDE) and a ZigBee protocol chip for physiological signal acquisition. To improve signal quality with low electrode-skin interface impedance, a silicon-based MDE is fabricated via micromachining technology. The proposed wireless sensor can provide four different channels for up to 10 kHz bandwidth, 10-bit resolution biomedical signal transmissions. Different from other systems, the proposed wireless sensor employs a novel power management method for physiological signals to reduce power consumption. The proposed wireless sensor successfully transmits electrocardiogram (ECG) signals and four-channel electroencephalogram (EEG) signals with power consumptions of 92.7 and 56.8 mW respectively. It consumes 46% less power than the original sensor without power management (173 mW) in ECG acquisition and 67% less power in EEG acquisition. The circuit printed-circuit-band area in the proposed wireless sensor is 3.5×4.5 cm, suitable for various portable biomedical applications.

This research shows the realization of 2.4-GHz film bulk acoustic wave (FBAW) filters. The design, simulation, fabrication, measurement, and analysis of the film bulk acoustic wave resonator (FBAR) devices are covered, which is helpful for the manufacture of the FBAR devices. The simulation of the FBAR and RF circuitry can be integrated on a single platform. The fabrication of the FBAW filters is compatible with complementary metal-oxide semiconductors. This device can be used in 2.4-GHz bandpass filters, such as 802.11b/g and Bluetooth. In this research, the 2.4-GHz FBAW filters for wireless communication have been accomplished. The fabricated FBAW filters have insertion loss of −10 dB, return loss of −7 dB, and stopband rejection of −25 dB, central frequency of 2.485 GHz, bandwidth of 60 MHz, and size of 0.5 mm×0.5 mm.

We present an ohmic series radio-frequency microelectromechanical system (RF MEMS) switch based on a moveable corrugated diaphragm that activates switch contact. Corrugation technology is introduced in the SiO₂/Si3N₄ diaphragm for reducing the residual stress in the diaphragm. Moreover, a multilayer metallization system containing ruthenium/gold is proposed as a contact metal to address the reliability of the switch contact. The concept of the corrugated diaphragm, together with a ruthenium/gold contact-metal system, is proven by the characterization of fabricated RF MEMS switches to be an effective way to realize reliable electric contact with significantly reduced pull-in voltage. The durability of the switch contact is increased significantly with the introduction of the multilayer metal, compared to a pure gold contact.

We report a multifunctional silicon micromachined gyroscope. The gyroscope can sense the rolling, yawing, and pitching angular velocity synchronously. Both the principle and the experiment of the gyroscope are presented to explain the multifunction. We also discuss the way to determine the deflecting direction and deflecting position of the rotating carrier in the gravitation field.

Investigations into infrared radiation transmission of periodic subwavelength Pd hole arrays reveal a transmittance attenuation of the main resonant peak upon exposure to hydrogen of the hole arrays. The attenuation is attributed to the formation of Pd hydride, which results in the combine effects of lattice expansion of the Pd film, generating a decrease in the hole width, and optical properties variations of the Pd film, giving rise to stronger damping of the surface plasmons. The reduction in the hole width of the arrays is estimated to be of the order of a few tens of nanometers. Our results illustrate the possibility of detecting minute changes in the structure of the metallic hole arrays by monitoring the transmittance of the resonant peaks. The all-optical hydrogen sensing scheme presented in this work is thought to find applications in the detection of hydrogen at concentration levels near the lower flammability threshold for alarm purposes.

Longitudinally driven giant magnetoimpedance (GMI) effect has been measured in Fe_73.5Cu₁Nb₃Si_13.5B₉ ribbons, and the enhancement of GMI effect using magnetoelastic resonance was investigated. The results showed that at a certain driven frequency when magnetoelastic resonance occurred, there was a great enhancement of the impedance of the element and MI effect. For the ribbon of 1.0 cm in length annealed at 480°C, the maximum MI ratio of 10 906% was achieved at the frequency of 214 kHz. The maximum sensitivity reached up to 5 155%/Oe, which was almost 40 times higher than that observed in traditional MI measurements. The results demonstrated that the enhanced magnitude of MI effect mainly depended on magnetoelastic coupling coefficient k.

We determine single-wall carbon nanotube (SWCNT) thermal conductivity and tunable flattening dynamics at heat flux ranging from 0.01 to 0.3 W/m² subject to different thermal loading of 5 to 50 K/nm, using a nonequilibrium molecular dynamics (MD) simulation with true carbon potentials. The numerical model adopts Morse bending, a harmonic cosine, and a torsion potential. The applied Nosé-Hoover thermostate describes atomic interactions taking place between the atoms. Hot and cold temperature reservoirs are respectively imposed on both computational domain sides to establish the temperature gradient along the carbon nanotube. Atoms at the interface exhibit transient behavior and undergo an exponential type decay with exerted temperature gradient. The thermal impact causes system fluctuation in the initial 3 ps leading to a transport region temperature as high as 600 K. The thermal relaxation process reduces impact energy influence after 30 ps and leads to Maxwell's distribution. Steady-state constant heat flux is observed after thermal equilibrium. Furthermore, the temperature curves show distinct high disturbance at initial time and linear distribution along the tube axial direction after steady state. Results suggest that thermal conductivity value increases with increasing CNTs subjected to thermal loading up to a temperature gradient of at least ~41.3 K/Å, representing thermal gradient convergence at heat conduction value 1258 W/mK. Simulation results yield precise understanding of nanoscale transient heat transfer characteristics in a single-wall carbon nanotube. Last, it is shown that given a thermal loading of sufficient intensity, the initial round cross section of the hot end of the nanotube transits through a series of triangular-like states to a flattened, rectangular configuration. As time elapses, the cross section oscillates between two fully perpendicular flattened states at a frequency that increases linearly with the intensity of the applied thermal load. (Cont'd.)

Traditional ribbon microphones cannot be miniaturized owing to the sensitivity of the microphone in proportion to its ribbon length. A novel symmetrical voice coil instead of the traditional ribbon is proposed, designed, and optimized. The new structure of ribbon microphones was fabricated by microelectromechanical systems (MEMS) technology, which allows increasing the effective coil length while reducing the diaphragm dimension. The obtained results present a voice coil length of 77.5 mm under a limited ribbon length of 17 mm. Compared with the conventional ribbon microphones (with ribbon length 50 mm and voice coil length 50 mm), the diaphragm dimension was reduced but its effective length was increased by about 55%, from 50 mm to 77.5 mm. Moreover, the magnetic flux density in the air gap of the magnetic circuit by simulations and experiments is measured to be at 5.1 and 5 kG, respectively.

A novel multistep loading and demolding process in nanoimprint lithography (NIL) with a soft mold is developed to fabricate 3-D micro- or nanoscale cathode structures in polymer photovoltaic (PPV) devices. Experiments show that this new NIL process, called distortion reduction by pressure releasing (DRPR) and two-step curing method for the demolding process, can reduce and avoid the distortions of the imprint mold and wafer stage, and through the two-step curing method, the transformation of resist from liquid to solid state can be controlled, which is helpful to decrease the demolding force and avoid some defects caused by "blind" demolding. With this new NIL process, the main replicating error caused by distortions and blind demolding can be limited effectively, and the micro- or nanoscale cathode structures in PPV devices can be fabricated with high fidelity to the imprint mold, which can improve the power conversion efficiency of PPV.

With the development of MEMS, micropower has gradually become one of the essential problems in MEMS applications. The structure of the selective emitter radioisotope microbattery is investigated in detail. The working principle of a radioisotope microbattery is discussed at first. Then the design of the radioisotope microbattery is proposed around the aspects of shape structure and doping mode. Next, a prototype of the radioisotope microbattery in three different shape structures with two doping modes is fabricated. Finally, the prototype of the radioisotope microbattery is tested at Beijing Atom HighTech Incorporated. After comparing the selective emitter radioisotope (SER) microbattery and back surface field (BSF) microbattery, the results indicate the characteristic of the SER microbattery has better performance with the type of inverted pyramid array and V channel array.

In this study, an electromechanical modeling technique for characterization and optimization design of the postcomplementary-metal-oxide-semiconductor (pCMOS) capacitive microarrayed ultrasonic transducer (CMUT) is presented. A two-dimensional, axisymmetric finite element model is developed using the ANSYS parametric design language. Electromechanical simulations are performed to investigate the fundamental characteristics of the CMUT, such as collapse voltage, resonant frequency, capacitance, and electromechanical coupling coefficient. Both the numerical and analytical (experimental) results agree well to show the validity of the proposed approach. The study of the influence of each defined parameter on the collapse voltage and resonant frequency is also presented. An integrated design approach that couples the genetic algorithm (GA) with the commercial finite element method (FEM) software ANSYS is developed to obtain the best design parameters. The optimal results show that the design objective with the equality constraint, which are to minimize the collapse voltage while simultaneously achieving the customized resonant frequency, are satisfied. From the presented results, it is concluded that the GA/FEM coupling approach provides another useful numerical tool for multiobjective design of the pCMOS-CMUT.

This PDF file contains the editorial “Guest Editorial: Extreme Ultraviolet Interference Lithography” for JM3 Vol. 8 Issue 02

Recently, extreme ultraviolet interference lithography using a single grating interferometer and a highly coherent synchrotron insertion device source has proven to be an extremely useful technique for producing patterns with feature sizes in the range of 10 nm. The high demand for these nanoscale patterns and the small number of suitable highly coherent extreme ultraviolet sources has created new interest in the cascaded grating interferometer because of its relaxed demands for spatial and temporal coherence. This work extends that of earlier researchers on such systems by providing a compact algebraic analysis of the effects on fringe contrast of source divergence, spectral bandpass, lack of parallelism of the grating rulings, grating period mismatch, defocus, and wavefront curvature. The results are applied to illustrate the feasibility of implementing the interferometer on a small bending magnet synchrotron source, but the analysis should be applicable to typical portable plasma sources as well.

Extreme ultraviolet interferometric lithography (EUV-IL) is a powerful nanopatterning technique, exploiting the interference of two beams of short-wavelength radiation (λ≈13 nm) to form high-accuracy fringe patterns. Transmission diffraction gratings of appropriate period (40−100 nm) are used to form the beams; the substrate is located in the region of overlap to expose the photoresist material, recording 20−50 nm interference fringe patterns. Although the physics of EUV-IL is simple, its actual implementation is not and requires attention to detail in order to fully exploit the power of the technique. In order to understand the impact of realistic physical conditions on the performance of EUV-IL, we have developed a set of accurate numerical models based on the Rayleigh-Sommerfeld diffraction theory. These modeling tools are then applied to generate a complete and accurate analysis of EUV-IL, taking into account all the relevant physical processes, from finite extent of the gratings to the partial coherence of the source, and including detailed physical structure of the mask. The results are used to guide the design and implementation of EUV-IL exposure systems, down to the sub-11-nm range.

We review the performance and applications of an extreme ultraviolet interference lithography (EUV-IL) system built at the Swiss Light Source of the Paul Scherrer Institut (Villigen, Switzerland). The interferometer uses fully coherent radiation from an undulator source. 1-D (line/space) and 2-D (dot/hole arrays) patterns are obtained with a transmission-diffraction-grating type of interferometer. Features with sizes in the range from one micrometer down to the 10-nm scale can be printed in a variety of resists. The highest resolution of 11-nm half-pitch line/space patterns obtained with this method represents a current record for photon based lithography. Thanks to the excellent performance of the system in terms of pattern resolution, uniformity, size of the patterned area, and the throughput, the system has been used in numerous applications. Here we demonstrate the versatility and effectiveness of this emerging nanolithography method through a review of some of the applications, namely, fabrication of metallic and magnetic nanodevice components, self-assembly of Si/Ge quantum dots, chemical patterning of self-assembled monolayers (SAM), and radiation grafting of polymers.

Extreme ultraviolet interference lithography (EUV IL), especially in combination with tool-independent metrics for resist performance, is a powerful technique for judging progress with current resists, the potential of new materials and studying the fundamentals of resist performance. We provide an overview of how EUV IL is applied for resist testing and early material selections. Also discussed are examples of EUV IL being used to gain fundamental understanding for resist characterization under EUV imaging conditions.

The development of tabletop extreme ultraviolet (EUV) lasers opens now the possibility to realize interferometric lithography systems at EUV wavelengths that easily fit on the top of an optical table. The high degree of spatial and temporal coherence and high brightness of the compact EUV laser sources make them a good option for interferometric applications. The combination of these novel sources with interferometric lithography setups brings to the laboratory environment capabilities that so far had been restricted exclusively to large synchrotron facilities.

A small-scale interferometric EUV exposure system is presented, based on Talbot interferometric imaging. In this approach, illuminated EUV grating mask orders are recombined remotely through reflection, resulting in interference with spatial preservation across the image plane. The approach is achromatic for NA=λ/p using parallel recombination mirrors and is superior to other methods when efficiency and alignment tolerances are considered. The system design is compatible with both a compact EUV plasma source, which can yield exposure times on the order of several minutes per field, and a compact resonant cavity EUV laser source, which can produce exposure times on the order of several seconds. The system is capable of resolution to 15 to 30-nm half-pitch and is adjustable to accommodate targeted values in this range. Field size is approximately 1 mm, which is consistent with the current field size offered on 193-nm immersion interferometric systems. Wafer stage technology allows for nanometer positioning control across the field and through a field depth of over 50 µm. EUV mask grating fabrication requirements are within the current state of the technology, where no grating component requires resolution better than 2× the image plane pitch (a full-frequency doubled system). Reflection technology has been utilized for each component of the interferometer unit. While the grating mask employs (SiMo)⁴⁰ multilayers, the interferometric turning mirrors are metallic coatings at angles sufficient to achieve reflection efficiencies greater than 80% for 15-nm half-pitch resolution. The efficiency of the interferometric head is between 7 and 29%, much higher than that which can be achieved using other interferometric lithography (IL) methods. Vibration control for the EUV-IL15 is achieved through a state-of-the-art piezoelectric active isolation system to achieve vibration criteria levels at 1/3 vibration control level E.

Double-patterning generation at 32-nm node and beyond raises many subjects for photomask blanks. We especially focus on the resolution improvement by hyper-thin resist combined with the hardmask process called the hyper-thin resist system (HTRS). Cr-hardmask has been specially developed for the HTRS, and this Cr material shows an extremely high etching rate. Additionally, we confirmed that a 55-nm resist thickness was available to etch the Cr-hardmask and last then the resolution of MoSi-absorber patterns was improved by HTRS, such as 45-nm LS, 60-nm isolated line and hole, and 35-nm isolated space. Moreover, the Cr-hardmask showed almost no film stress, which is necessary to achieve the image placement accuracy required for the double patterning. MoSi-binary with HTRS meets the photomask technology requirements for 32-nm node and beyond.

We have developed a number of second-generation high-index candidate immersion fluids that exceed the 1.6 refractive index requirement for immersion lithography at 193 nm to replace the water used in first-generation immersion systems. To understand the behavior and performance of different fluid classes, we use spectral index measurements, based on the prism minimum deviation method, to characterize the index dispersion. In addition to fluid absorbance and index requirements, the temperature coefficient of the refractive index is a key parameter. We have used a laser-based Hilger-Chance refractometer system to determine the thermo-optic coefficient (dn/dT) by measuring the index change versus temperature at two different laser wavelengths, 632.8 and 193.4 nm. Also, we determined the batch-to-batch (within a 6-month period), before and after irradiation (at 193.4 nm), before and after air exposure, and before and after resist exposure (image printing test) variations of index and Δn/Δλ. The optical properties of these second-generation immersion fluids mostly compare favorably to water; the ratio of index of refraction at 193.4 nm is 1.644/1.437, the dispersion from d-line (Δn_193-d) is 0.160 versus 0.103 and dn/dT at 193.4 is −550×10⁻⁶/K vs. −93×10⁻⁶/K, respectively.

Traditional double-exposure lithography (DEL) or double-patterning lithography (DPL) methodologies stem most from the resolution enhancement standpoint. A single mask with high feature densities is split into two exposure steps, each with lower feature densities that can be easily resolved. The DEL is proposed as the process window enhancement technology for sub-110-nm technology. Features with sparse pitches are printed by a first step of dense pitch exposures and a second exposure with dummy features removed. The pattern decomposition strategy described is similar to that of subresolution assisting features (SRAF). So it is compatible with the traditional rule-based SRAF implementation methodology. By comparing the depth of focus (DOF) of the 110-nm lithography process between the single exposure and the double exposure, it is found that the DOF for marginal features is extended by using double-exposure methodology, and thus extends the capability of KrF exposure tools. Furthermore, the link between the overlay performance and the overlap of the second exposure's trim slots over the first exposure is studied. The results show that the overlay control is within the KrF scanner capability. As a further study, the proposed double-exposure methodology for the 90-nm lithography process is evaluated.

Thermoelastic damping and fluid damping may collectively affect the resonant behaviors of silicon resonators. A finite element model is developed to predict the characteristics of the out-of-plane resonance, and the results are verified by experiments. The implementation of the perturbation method leads to an eigenvalue equation, from which the resonant frequency and the quality factor can be evaluated. The fluid damping problem is formulated by augmenting the governing equation with a linear damping term, whose coefficient is inversely determined from the experimental correlations. With the incorporation of the fluid damping term, the computational prediction achieves a good agreement with the experiment. The same method can also be extended to study the in-plane vibration of beam resonators.

A novel computer security authentication system is proposed to improve computer security. There are two main differences between the novel system and the conventional one. First, the key is a physical code that is stored in counter meshing gears (CMEs). Second, the user's password is discriminated by a microelectromechanical systems (MEMS) coded lock. This system is composed of a MEMS coded lock, a peripheral component interconnect (PCI) card with a printed circuit board (PCB), and software in a basic input/output system (BIOS) chip. Unlike the old MEMS coded lock, two reset micromotors and an optoelectronic coupler are installed in the new MEMS coded lock. The circuit of the PCI card with PCB, which is used to drive the four micromotors of the lock, is developed. The software is assembled by netwide assembler (NASM) and written into the BIOS chip. Testing of the prototype shows that the MEMS coded lock can discriminate the user's password effectively. If the user's password is matched with the physical code, permission to use the computer is granted; otherwise, it is locked up.

We describe the design and experimental characterization of two optimized thermal actuators devised to operate by means of scavenging heat from the environment. Different from the traditional MEMS thermal actuator that relies on electric current to generate heat by Joule effect, the devices presented here are optimized to absorb external heat and convert it into mechanical displacement and force. The behavior of vertical and horizontal microactuators fabricated in a standard surface micromachining process (PolyMUMPs, Research Triangle Park, North Carolina) demonstrates the viability of exploiting heat from the surrounding medium to realize batteryless microsystems. Analytical and finite element models are provided in support of the design. Results show that fairly large and useful displacements can be achieved at commonly available operating temperatures.

Reaction-diffusion chemical systems where the catalyst of the reaction is the only diffusing species are investigated. Here, the correlation length and Hurst roughness exponent are derived in one-, two-, and three-dimensional first-order catalytic reaction-diffusion problems. These results are relevant to many chemical systems, and in particular to chemically amplified photoresists used in semiconductor lithography, where the correlation length and Hurst exponent affect the line-edge roughness of sub-100-nm printed features.