D.F. Moore

SU-8 thick photoresist processing as a functional material for MEMS applications

The use of SU-8 high aspect ratio, thick, photoresist as a functional material for MEMS applications is described in this paper. SU-8 processing is developed to implement low-stress SU-8 structures as permanent and functional material incorporated with silicon-on-insulator technologies. Silicon micromachined cantilevers were fabricated with SU-8 structures on the cantilevers as added masses. Separation of material function can be achieved in this way. Silicon provides excellent mechanical properties, while SU-8 is used as extra mass to adjust the mechanical behaviour. The resonance behaviour of the cantilever structure with SU-8 is characterized through measurement, simulation and calculation, and the strength of the SU-8 material for this purpose is evaluated. The results show that SU-8 is well suited as a permanent material in mechanically active MEMS devices, and several applications are suggested. 3D MEMS architectures can also be achieved in this manner.

Characterization of three-dimensional microstructures in single-crystal diamond

We report on the Raman and photoluminescence characterization of three-dimensional microstructures fabricated in single crystal diamond with a Focused Ion Beam (FIB) assisted lift-off technique. The fabrication method is based on MeV ion implantation, followed by FIB micropatterning and selective chemical etching. In a previous publication we reported on the fabrication of a micro-bridge structure exhibiting waveguiding behavior [P. Olivero, S. Rubanov, P. Reichart, B. Gibson, S. Huntington, J. Rabeau, Andrew D. Greentree, J. Salzman, D. Moore, D. N. Jamieson, S. Prawer, Adv. Mater., 17 (20) (2005) 2427]. In the present work, Raman and photoluminescence spectroscopies are employed to characterize the structural quality of such microstructures, particularly as regards the removal of residual damage created during the machining process. Three-dimensional microstructures in high quality single crystal diamond have many applications, ranging from integrated quantum-optical devices to micro-electromechanical assemblies.

Young's modulus measurement of thin-film materials using micro-cantilevers

The need for a simple and effective characterization technique for thin-film materials which are widely used in MEMS (micro-electro-mechanical systems), using commonly available equipment, has prompted consideration of cantilever beam-based methods. The advantages of this class of techniques which employ a scanning surface profiler to deform micro-cantilevers are simplicity, speed, cost and wide applicability. A technique for extracting Youngs modulus from static deflection data is developed in this paper and validated in experiments on thin-film specimens of silicon nitride deposited on a silicon substrate under different conditions. Finite element analysis is used to assess the influence of factors affecting the bending of thin films, and thus guide the analysis of micro-cantilever deflection data for reliable characterization of the material.

High-T/sub c/ Josephson junctions by electron beam irradiation

Josephson junctions were produced by electron beam irradiation of patterned YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin film tracks on MgO substrates. Single weak links show Fraunhofer-type critical current behavior as a function of field (I/sub c/(H)), indicating reasonable current uniformity across the junction. Simple low inductance superconducting quantum interference devices (SQUIDs) have also been made with greater than 70% critical current modulation at 25 K. The relatively high critical current density of these weak links means that it is possible to observe a crossover from small to large junction behavior at a temperature only a few degrees below the T/sub c/ of the junction. In the small junction regime the current-voltage (I-V) curve can be fitted by the resistively shunted junction (RSJ) model, whereas in the large junction regime the I-V curves change to be non-RSJ-like. The I/sub c/R/sub n/ (critical-current normal-resistance) product is typically around 0.05-0.2 mV at temperatures a few degrees below the T/sub c/ of the junction and, for a junction with high T/sub c/, can reach 1 mV at 4.2 K.<<ETX>>

Electron beam damaged high-T/sub c/ junctions-stability, reproducibility and scaling laws

The problems of stability and reproducibility of the electron beam irradiated high-T/sub c/ junctions have been studied. It is found that with a overdamage-anneal protocol that stable junctions can be obtained. While on chip uniformity can be very good (1%), the chip to chip reproducibility is not better than 20%. The annealing process allows us to vary T/sub c/ of the junctions over a wide range, making it possible to study the scaling behaviour of a single junction. We find that in these junctions I/sub c/R/sub n//spl prop/J/sub c//sup n/, with n=0.75-0.8 or, since the quasiparticle and Cooper-pair cross sections appear to be equivalent, I/sub c/R/sub n//spl prop//spl sigma//sub N//sup p/ where p=3.0-3.7.<<ETX>>

Optical MEMS for telecoms

Abstract Microelectromechanical systems (MEMS) are of increasing importance in optical systems, particularly for telecommunications applications. This paper presents a review of materials, fabrication technologies, and applications in two key areas: optoelectronic packaging and functional optical devices. In packages, the advantage of MEMS are their ability to provide accurate passive alignment features or optical surfaces at low cost. In devices, the attraction is the possibility of combining mechanical, electrical, and optical features in movable components that switch, attenuate, or filter light. These free-space components can, in many cases, out-perform their counterparts in bulk or guided wave optical formats. Components fabricated using the new discipline of MEMS are finding an increasing number of applications in sensors, devices, and actuators 1 , 2 . MEMS are being applied to a wide range of systems. Progress is dramatic, especially in optical telecommunications 3 . These applications may be divided roughly into two classes: i) those requiring precise features for optical alignment, and ii) those involving the small moving optical parts necessary for more advanced functionality.

Development of all metal electrothermal actuator and its applications

The in-plane motion of microelectrothermal actuator (heatuator) has been analysed for Si-based and metallic devices. It was found that the lateral deflection of a heatuator made of a Ni-metal is about -60% larger than that of a Si-based actuator under the same power consumption. Metals are much better for thermal actuators as they provide a relatively large deflection and large force, for a low operating temperature, and power consumption. Electroplated Ni films were used to fabricate heatuators. The electrical and mechanical properties of electroplated Ni thin films have been investigated as a function of temperature and plating current density, and the process conditions have been optimised to obtain stress-free films suitable for MEMS applications. Lateral thermal actuators have been successfully fabricated, and electrically tested. Microswitches and microtweezers utilising the heatuator have also been fabricated and tested.

Electron-beam damaged high-temperature superconductor Josephson junctions

Results are presented on the fabrication and characterization of high critical temperature Josephson junctions in thin films of YBa2Cu3O7−δ produced by the process of focused electron-beam irradiation using 350 keV electrons. The junctions so produced have uniform spatial current densities, can be described in terms of the resistive shunted junction model, and their current densities can be tailored for a given operating temperature. The physical properties of the damaged barrier can be described as a superconducting material of either reduced or zero critical temperature (Tc), which has a length of ∼15 nm. The Tc reduction is caused primarily by oxygen Frenkel defects in the Cu–O planes. The large beam currents used in the fabrication of the junctions mean that the extent of the barrier is limited by the incident electron-beam diameter, rather than by scattering within the film. The properties of the barrier can be calculated using a superconductor/normal/superconductor (SNS) junction model with no bound...

Realization and properties of YBa2Cu3O7−δ Josephson junctions by metal masked ion damage technique

We have developed a simple process to fabricate high-TC Josephson junctions by a combination of focused ion beam milling and 100 keV H2+ ion implantation. The resistively shunted junction-like current–voltage characteristics were observed in the temperature range of 48 to 4.2 K. The devices showed clear dc and ac Josephson effects. This technique is very promising in terms of simplicity and flexibility of fabrication and has potential for high-density integration.

Nano- and micro-technology applications of focused ion beam processing

Abstract Advances in focused ion beam technology including higher current density, finely focused beams under computer control are making micrornachining an excellent prototyping route for devices and a commercial possibility for production. This paper concentrates on new applications of focused ion beam processing in Si based microdevices and in sensors, including high-resolution patterning of YBaCuO superconducting Josephson junction devices.