Thin film shape memory alloy microactuators

Thin film shape memory alloys (SMAs) have the potential to become a primary actuating mechanism for mechanical devices with dimensions in the micron-to-millimeter range requiring large forces over long displacements. The work output per volume of thin film SMA microactuators exceeds that of other microactuation mechanisms such as electrostatic, magnetic, thermal bimorph, piezoelectric, and thermopneumatic, and it is possible to achieve cycling frequencies on the order of 100 Hz due to the rapid heat transfer rates associated with thin film devices. In this paper, a quantitative comparison of several microactuation schemes is made, techniques for depositing and characterizing Ni-Ti-based shape memory films are evaluated, and micromachining and design issues for SMA microactuators are discussed. The substrate curvature method is used to investigate the thermo-mechanical properties of Ni-Ti-Cu SMA films, revealing recoverable stresses up to 510 MPa, transformation temperatures above 32°C, and hysteresis widths between 5 and 13°C. Fatigue data shows that for small strains, applied loads up to 350 MPa can be sustained for thousands of cycles. Two micromachined shape memory-actuated devices-a microgripper and microvalve-also are presented     

Shape detection with limited memory

A new approach to shape detection through the generalized Hough transform is introduced. The method is based on a limited memory implementation of the transform, that reduces its cost and makes it suitable for hardware implementation. The rationale of the method is that a shape is bound by a circle whose radius is, in most practical situations, much smaller than the dimensions of the image processed. This a priori knowledge can be used during the vote collection phase of the transform to guide flushing operations against a filled memory. The method is tested in the simple case of circles detection and in more practical situations of IC inspection.     

Vertical comb array microactuators

A vertical actuator fabricated using a trench-refilled-with-polysilicon (TRiPs) process technology and employing an array of vertical oriented comb electrodes is presented. This actuator structure provides a linear drive to deflection characteristic and a large throw capability which are key features in many sensors, actuators and micromechanisms. The actuation principle and relevant theory is developed, including FastCap simulations for theoretical verification. Design simplifications have been suggested that enable one to use parallel plate analytical expressions which match simulation results with /spl sim/5.6% error. Several actuators were designed and fabricated using the 7-mask TRiPs technology with calculated drive voltages as low as 45 V producing 10 /spl mu/m of deflection. The actuators employed a mechanical structure that was 18 /spl mu/m tall using a polysilicon layer 1.5 /spl mu/m thick and occupying a total area of 750 /spl mu/m by 750 /spl mu/m. The actuators were successfully tested electrostatically and several microns of deflection were observed.     

Thermal bubble powered microactuators

Thermal bubble powered micro mechanical actuators have been successfully demonstrated in working liquids. Micro mechanical plates which function as the mechanical actuators are 70×60×2 m³ in size. They have been fabricated by surface-micromachining technology and suspended 2 m above the substrate by the supports of cantilever beams. Micro thermal bubbles which are generated by heavily phosphorus doped polysilicon line resistive heaters have been used to lift the mechanical plates in a controllable manner. The typical current required to generate a single, spherical thermal bubble as the actuation source on top of the micro line resistors (60×2×0.3 m³ in size) is 8.4 mA (80 m Watt) in FC 43 liquid (an inert, dielectrical fluid available from the 3M company). The thermal bubbles have been demonstrated to actuate the mechanical plate perpendicularly to the substrate with a maximum elevation distance of 140 m and a maximum actuation force of 2 N. This new actuation mechanism is expected to find applications for micro fluidic devices.The authors would like to thank Prof. V.P. Carey, Mechanical Engineering department, U.C. Berkeley and Dr. A.P. Lee for valuable discussions. The devices were fabricated in the UC Berkeley Microfabrication Laboratory and the FC liquid was provided by 3M company. This work has been supported by Berkeley Sensor and Actuator Center, an NSF/Industry/University Co-operative Research Center.     

Progress in magnetic microactuators

 Magnetic microactuator construction has benefited from two processing extensions: stacking in the vertical and horizontal direction and multiple X-ray mask sacrificial layer LIGA. Vertical stacking requires height control of electroplated structures. This has been achieved by material insensitive lapping and polishing techniques. Structural heights of more than 1 mm have been achieved with 300 μm low-energy exposures. This has resulted in actuators with output forces to 100 mN and throws to 2 mm. Re-planarization after electroplating without photoresist damage enables second layer photoresist application via solvent bonding and fly cutting. Exposure of the substrate with a second X-ray mask becomes useful if the second mask can be aligned to the substrate. This has been accomplished with sufficient accuracy via mechanical techniques. A variety of magnetic actuators have been constructed. All of them use assembled rather than integrated coils. The performance of the assembled coils is adequate for position sensing in linear actuators and has resulted in a closed loop control device. Received: 25 August 1997 / Accepted: 3 November 1997     

Electrothermally activated paraffin microactuators

A new family of electrothermally activated microactuators that can provide both large displacements and forces, are simple to fabricate, and are easily integrated with a large variety of microelectronic and microfluidic components are presented. The actuators use the high volumetric expansion of a sealed, surface micromachined patch of paraffin heated near its melting point to deform a sealing diaphragm. Two types of actuators have been fabricated using a simple three mask fabrication process. The first device structure consists of a 9 μm thick circularly patterned paraffin layer ranging in diameter from 400 to 800 μm all covered with a 4-μm-thick metallized p-xylylene sealing diaphragm. All fabricated devices produced a 2.7-μm-peak center deflection, consistent with a simple first order theory. The second actuator structure uses a constrained volume reservoir that magnifies the diaphragm deflection producing consistently 3.2 μm center diaphragm deflection with a 3-μm-thick paraffin actuation layer. Microactuators were constructed on both glass and silicon substrates. The actuators fabricated on glass substrates used between 50-200 mW of electrical power with response times ranging between 30-50 ms. The response time for silicon devices was much faster (3-5 ms) at the expense of a larger electrical power (500-2000 mW)     

Shape memory alloy based controllable multi-port microvalve

This paper describes an innovative miniature multi-port valve with a thin foil of shape memory alloy (SMA) as actuator for switching and dosing gaseous and liquid media. The normally closed (NC) microvalve has two structured SMA actuators that are switched independently of each other and either two inputs and one output or one input and two outputs. In addition to switching the media in the 3/4-way arrangement, it can also be used with a flow sensor in a closed loop control for dosing. Furthermore, the valve design is layer-based so that individual components can be manufactured according to given requirements or using different manufacturing technologies depending on the batch size. The SMA multi-port microvalve showed flow rates of about 2300 ml/min (nitrogen gas) and about 45 ml/min (water) for an applied pressure difference of 200 kPa and a heating current of about 400 mA. For flow regulation a closed loop control was realized and evaluated for a pressure difference of 100 kPa and a setpoint value of 900 ml/min.

     

Recent progress of microactuators and micromotors

This paper gives a concise review of IC-compatible micromachining technologies and various types of microactuators fabricated by such technologies. A system architecture oriented to micro systems is proposed. Promising fields of application are briefly overviewed.     

Magnetic microactuators based on polymer magnets

Integrated permanent magnet microactuators have been fabricated using micromachined polymer magnets. The hard magnetic material utilized is a polymer composite, consisting of magnetically hard ceramic ferrite powder imbedded in a commercial epoxy resin to a volume loading of 80%. The magnets have the form of thin disks approximately 4 mm in diameter and 90 μm in thickness. These disks have been magnetized in the thickness direction, and even in this geometrically unfavorable direction showed typical permanent magnet behavior with an intrinsic coercivity H_ci of 4000 Oe (320 kA/m) and a residual induction B_r of 600 Gauss (60 mT). Cantilever beam-type magnetic actuators carrying a screen-printed disk magnet on their free ends have been fabricated on an epoxy board. A planar coil on the opposite side of the substrate is used to drive the beams vertically. The actuators exhibit hard magnetic behavior allowing both attraction and repulsion by reversing the current direction. Static and dynamic testing of the magnetic actuators have been performed. The experimental data are compared with theoretical results obtained from both finite element simulations and analytical models. Good agreement is obtained between simulation and experiment     

微传感器和执行器的计算机模拟技术

介绍了计算机模拟技术在微传感器和微执行器设计中的应用 ,通过对多晶硅压力传感器和微泵膜片的计算机模拟分析 ,优化了器件的结构设计。研究工作表明计算机模拟是微传感器和微执行器设计的有效工具     

Optimal design analysis of electrothermally driven microactuators

This paper explores a comparative study between different designs of electrothermal microactuators with emphasis on optimal design and performance key factors. For this purpose, two typical designs for electrothermal microactuators with the same material properties are studied: one with different beam lengths (design A), other one with different beam sections and a flexure part (design B). Analytical model and finite element model (FEM) have been developed and validated by comparison of simulation results with experimental results in literature. Optimal geometrical dimensions to achieve maximum deflection have been obtained using genetic algorithm (GA). As the key factors, temperature distribution, power consumption and deflection of these microactuators have been compared in the range of microactuator functionality. Design B is more sensitive to geometrical dimension variation. Using optimal geometrical dimensions, an increase of almost 40 and 55% has been achieved for design A and B tip deflections, respectively. The modified design A with a gold layer results to an increase of 70% for tip deflection comparing to its optimal design.     

Micromixing and flow manipulation with polymer microactuators

Polymer actuators based on Gold/PolyPyrrole bilayers were microfabricated and their properties tested for flow promoting in the microdomain. When implemented in microchannels these actuators behaved as efficient micromixers for both, flow-through and stagnant conditions. Particle tracking experiments and numerical simulations of cross-sectional domains verified the capacity of these devices to promote complex, high velocity flows with chaotic advection properties in microscopic environments. Thinner devices could be actuated at higher frequencies than thicker devices, up to 10 Hz for 10 nm thick Gold layers with voltages not over 0.6 V (vs. Ag/AgCl), which led to enhanced flow generation properties. The results herein demonstrate that these actuators are practical candidates for fluid manipulation in the microdomain (for applications such as micromixing and pumping, and possibly even for propelling of swimming microdevices).     

Power delivery and locomotion of untethered microactuators

The ability for a device to locomote freely on a surface requires the ability to deliver power in a way that does not restrain the device's motion. This paper presents a MEMS actuator that operates free of any physically restraining tethers. We show how a capacitive coupling can be used to deliver power to untethered MEMS devices, independently of the position and orientation of those devices. Then, we provide a simple mechanical release process for detaching these MEMS devices from the fabrication substrate once chemical processing is complete. To produce these untethered microactuators in a batch-compatible manner while leveraging existing MEMS infrastructure, we have devised a novel postprocessing sequence for a standard MEMS multiproject wafer process. Through the use of this sequence, we show how to add, post hoc , a layer of dielectric between two previously deposited polysilicon films. We have demonstrated the effectiveness of these techniques through the successful fabrication and operation of untethered scratch drive actuators. Locomotion of these actuators is controlled by frequency modulation, and the devices achieve maximum speeds of over 1.5 mm/s.     

Fabrication of functional components for electromagnetic microactuators

With basic components for active drive systems (like coils, magnetic components like yokes and cores, and guides) available and their fabrication processes well established, the emphasis shifts to further optimize them. This may be accomplished by applying new materials or by further improving the fabrication technologies. This paper presents recent developments in the field of materials and technologies for components of the microactuator drive systems, as well as the latest results in optimizing the microactuator’s guides.     

Shape memory alloys and their application in structural oscillations attenuation

The paper investigates the benefits that the SMA-behaviour can introduce in the dynamical response of a structural system.The influence of SMA tendons contributing to the overall strength of a simple elastic–plastic structural model undergoing horizontal shaking and subject to vertical loads is firstly analysed, proving that coupling super-elastic members with elastic–plastic structures yields an excellent performance in attenuation both of the P–Δ effect and of the final residual deformation.In the second investigation, this system is looked at as an isolation device and is introduced in a m.d.o.f. elastic–plastic structural model; its attitude in suppressing plastic deformations in the super-structure is demonstrated.     

Hard and soft magnetic materials for electromagnetic microactuators

An important aspect of the development of electromagnetic microactuators is the search for suitable materials as well as the development of the respective deposition and patterning processes. Within the Collaborative Research Center 516 “Design and Fabrication of Active Microsystems”, it is the task of the subproject B1 “fabrication of magnetic thin films for electromagnetic microactuators” to perform these investigations. The materials of interest can be divided into two groups: hard magnetic materials and soft magnetic materials. Materials with optimized properties and fabrication processes have been developed within both groups. An example is Samarium–Cobalt (SmCo), which can either be deposited using magnetron sputtering as Sm₂Co₁₇ with a very high energy product or in the SmCo₅ phase using gas flow sputtering with very high deposition rates. In the area of soft magnetic materials, investigations on Nickel-Iron (NiFe) especially NiFe81/19 were followed by the evaluation of NiFe45/55, which features a higher saturation flux density B _s and relative permeability μ _r. Furthermore, current investigations focus on Cobalt-Iron (CoFe) and its further increased saturation flux density B _s and relative permeability μ _r. Current tasks include the stabilization of the fabrication processes to achieve good material properties (i.e. electroplating of CoFe) or a shortening (e.g. by using heated substrates during deposition) by using process alternative not used so far. Another topic is the integration into fabrication processes, i.e. the investigation of process stability and compatibility.     

Laterally driven electrostatic repulsive-force microactuators usingasymmetric field distribution

We present a new electrostatic actuation method using a lateral repulsive-force induced by an asymmetric distribution of planar electrostatic field. The lateral repulsive-force has been characterized by a simple analytical equation, derived from a finite element simulation. Quality-factors are estimated from the computer simulation based on creep flow model. A set of repulsive-force polycrystalline silicon microactuators has been designed and fabricated by a four-mask surface-micromachining process. Static and dynamic response of the fabricated microactuators has been measured at the atmospheric pressure for the driving voltage range of 0-140 V. The static displacement of 1.27 μm is obtained at the dc voltage of 140 V. The resonant frequency of the repulsive-force microactuator increases from 11.7 kHz to 12.7 kHz when the dc induction voltage increases from 60 V to 140 V. The measured quality-factors are increased from 12 to 13 in the voltage range of 60-140 V. Fundamental characteristics of the force, frequency and quality-factor of the electrostatic repulsive-force microactuator have been discussed and compared with those of the conventional electrostatic attractive-force microactuator     

Integrated electromagnetic microactuators with a large driving force

This paper describes a high power electromagnetic microactuator fabrication method that combines the hard magnetic Fe/Pt process, Ni/Fe permalloy magnetic circuit design, bulk micromachining, and excimer laser ablation. The hard magnetic material Fe/Pt is deposited under low temperature less than 350°C by sputter onto a suspension diaphragm to produce a perpendicular magnetic anisotropic field. The magnetic circuit with closed loop design is applied to concentrate the magnetic flux and increase the magnetic force. The magnetic field induced by the planar coil and Ni/Fe permalloy enhances the interaction with Fe/Pt to induce attractive and repulsive displacement, provide large output force, and operate at high frequency. This high power electromagnetic microactuator is demonstrated with minimum dimensions with a magnetic force two times greater than conventional magnetic micro-actuators.     

Analysis of the dynamics in microactuators using high-speed cinephotomicrography

This paper discusses the visualization of microdevice dynamics using high-speed cine photomicrograph. The visualization results in image sequences, which contain the kinematic position data of the moving parts in a microsystem. Utilizing a mathematical model, it is shown in this paper how to extract information about the forces and torques acting on the microdevice. Furthermore, the values of system parameters can be calculated if a dynamic model of the process is available and the identification of the parameters is unambiguous. In this paper, the model-based evaluation of high-speed-cinematographic image sequences is demonstrated for a microturbine and a microrelay. The measurements on the microturbine have been performed with a setup, which allows an image frequency up to 100 million frames per second for nonreproducible processes. The measurements of the microrelay have been taken with a second experimental setup using the stroboscopic principle. In the case of the microrelay, the complete identification of the dynamic model used by us is carried out. A first application of our identified model is the design of an optimal current pulse for the microrelay to damp oscillations     

A fabrication process for electrostatic microactuators withintegrated gear linkages

A surface micromachining process is presented which has been used to fabricate electrostatic microactuators. These microactuators are interconnected with each other and linked to other movable microstructures by integrated gear linkages. The gear linkages consist of rotational and linear gear structures, and the electrostatic microactuators include curved electrode actuators, comb-drive actuators, and axial-gap wobble motors. The micromechanical structures are constructed from polysilicon. Silicon dioxide was used as a sacrificial layer, and silicon nitride was used for electrical insulation. A cyclohexane freeze drying technique was used to prevent problems with stiction. The actuators, loaded with various mechanisms, were successfully driven by electrostatic actuation. The work is a first step toward mechanical power transmission in micromechanical systems