Q2M Special Session
Batch Fabrication Methods for Polymer Based Active Microsystems using Hot Embossing and Transfer Bonding Technologies
T. Grund, M. Heckele and M. Kohl
Forschungszentrum Karlsruhe GmbH, Institute for Microstructure Technology (IMT),Postfach 3640, 76021 Karlsruhe, Germany
Abstract
A batch compatible process flow to overcome the costly piece by piece assembly of hybrid microsystems is shown. Hot embossing is used to fabricate microstructured polymer layers. Wafer scale compatible bonding tasks are carried out by ultrasonic welding and heat activated bonding with micromachined bonding foils. As demonstrator device, a shape memory alloy (SMA) actuated polymer microvalve is introduced. The valve concept, fabrication technologies and device characteristics are discussed.
Fabrication of piezoelectric thick-film bimorph micro-actuators from bulk ceramics using batch-scale methods
R.P.Jourdain and S.A.Wilson
Materials Department, School of Applied Sciences, Cranfield University, Cranfield, Bedfordshire, MK43 0AL, United Kingdom
Abstract
Piezoelectric ceramic films in the 20-60 micron thickness range are rarely employed today in commercial micro-mechanical devices, even though their expected force capability suggests that they are well suited to many micro-fluidic and micro-pneumatic applications. Some examples would be micro-scale fuel cells and micro-combustors. Head sliders, radio-frequency (RF) micro-switches and powered micro-optics are further potential application areas. These are only a few and the barriers in bringing them into reality are those of processing compatibility rather than commercial desirability. Such issues are being addressed in the EU Framework 6 Project ‘Q2M’, which focuses on batch-scale fabrication issues for high quality new micromechanical devices that are cost-effective and which have extended capabilities.
This paper discusses a potential batch-scale production route for piezoelectric thick-film bimorph microactuators that combines ultra-precision grinding of ceramics and femto-second laser machining, along with standard micro-fabrication techniques such as wafer bonding. This new method has the key advantage that many different shapes and thicknesses of actuator can be made with only minor process changes, meaning that actuators can be designed to suit their intended application. It contrasts with current practice whereby micro-actuators are often designed around a limited range of standard components, with consequent reduction in their achievable performance. The examples used are a 6mm diameter plane-spiral bimorph actuator for integration into a polymeric micro-valve and 2-5mm long bimorph cantilevers intended for use in
a new type of silicon ‘house’ micro-valve, with pneumatic applications.
Material aspects for batch integration of PZT thin films using transfer bonding technologies – Q2M development
D. Bhattacharyya (a), R. V. Wright (a), Q. Zhang (a), P.B. Kirby (a), R. Guerre (b), U. Drechsler (b), M. Despont (b), F. Saharil (c), J.Oberhammer (c)
(a) Materials Department, Cranfield University, Bedford MK43 0AL, UK
(b) IBM Research Gmbh, Zurich Research Laboratory, Rueschlikon, Switzerland
(c) Microsystem Technology Lab, KTH – Royal Institute of Technology, Stockholm, Sweden
Abstract
Transfer bonding is a reliable cost-efficient and low-temperature CMOS compatible technique which allows batch integration of materials whose incompatibility with Si makes them unsuitable for monolithic integration. In this heterogeneous device integration method the material and process incompatibilities inherent in Si IC technology are overcome by fabricating devices on separate substrates and then transferring them onto target (e.g. CMOS) wafers. Transfer bonding has great potential for integrating RF-MEMS devices incorporating, for example, high thermal budget materials such as PZT and PST or non-ferroelectric piezoelectrics such as AlN and ZnO into microwave ICs for enhanced systems performance. This paper presents an overview of technology developments within the EU sponsored project Q2M for the realization of transfer bonded piezoelectrically actuated RF MEMS switches and other components focusing in particular on material factors relating to growth of the piezoelectric films, in this case sol-gel deposited PZT, that restricts the choice of device layers and impact on PZT properties such as microstructure, film orientation and piezoelectric coefficients. New process developments such as hard masking of PZT pattern during RIE etching and its compatibility with polymer transfer bonding are discussed.
The integration of mono-crystalline silicon micro-mirrors on CMOS for SLM applications
F. Zimmera, M. Friedrichsa, M. Lapisac, F. Niklausc, M. Muellera, T. Bakkeb, H. Schenka, H. Laknera
a Fraunhofer Institute for Photonic Microsystems (IPMS), Maria-Reiche-Str. 2, D-01109 Dresden, Germany
b SINTEF Department of Mikrosystems and Nanotechnology, Gaustadalleen 23C, Oslo, Norway
c KTH, The Royal Institute of Technology, Stockholm, Sweden
Abstract
Spatial light modulators (SLMs) based on micro-mirrors for use in DUV lithography and adaptive optics need very high mirror planarity as well as mirror stability. We will present results of new micro-mirror arrays, consisting of monocrystalline silicon, which is a material to fulfil these requirements. As all mirrors of the SLM can be separately activated by an underlying CMOS circuit, the integration of CMOS and MEMS must be achieved, which results in certain restrictions on processing temperatures and the compatibility of materials. Therefore a special low temperature bonding technology has been developed, using an adhesive polymer. This technique provides the transfer of a 300nm thin mono-crystalline silicon layer to the CMOS wafer using only 250°C. First silicon micro-mirrors have been made and characterized using pure adhesive polymer (PMGI), improvements using a mix of an inorganic material with a thin bond-polymer benzocyclobutene BCB) on top are in development. Both approaches and their results will be discussed and presented in detail.
Towards Batch Integration of SMA into Microsystems: An Actuator Prototype
D. Clausi, J. Peirs, D. Reynaerts
Katholieke Universiteit Leuven, Department of Mechanical Engineering, Division PMA
Abstract
Shape Memory Alloys have a considerable potential for integration into microsystems, where scaling down of their size allows favorable exploitation of the intrinsic adaptive capabilities, providing an actuation mechanism for applications (e.g. micropneumatics) requiring large force control and large actuator stroke. However, the implementation of these materials into actual structures is rather complex and mostly confined to depositing thin NiTi films onto certain target substrates, resulting in devices having a relatively high cost-per-piece. This paper is aimed at investigating a novel approach for batch integration of SMA to microactuators, which might provide a cost-effective alternative to thin film technology while enhancing functional properties and design flexibility. Indicative requirements for the actuator design have been drawn from typical microvalve applications. In order to evaluate the actuator performance, brass microcantilevers have been produced, with prestrained SMA thin wires bonded on top of them, eccentrically with respect to the cantilever’s neutral plane. The activation of SMA element is obtained by direct heating through electrical current. The bending actuation of the cantilever leads to large strokes, expected to match the requirements of a wide range of applications.
Wafer-scale manufacturing of robust trimorph bulk SMA microactuators
N. Sandström (a), S. Braun (a), T. Grund (b), G. Stemme (a), M. Kohl (b), W. van der Wijngaart (a)
a Microsystem Technology Lab, KTH - Royal Institute of Technology, Stockholm, SWEDEN
b Institut für Mikrostrukturtechnik, Forschungszentrum Karlsruhe GmbH, Karlsruhe, GERMANY
Abstract
This paper demonstrates the concept of wafer-level fabrication and integration of robust bulk SMA microactuators based on adhesive bonding of cold-rolled SMA sheets to silicon wafers. Contact printing of an adhesive polymer ensures a selective bonding when transferring full SMA sheets to silicon structures on a patterned wafer. The induced stress of a thin dielectric film deposited on top of the SMA sheet ensures a stable and built-in reset mechanism of the actuators. The trimorph microactuators can be actuated by indirect resistive heating through a thin metal film. We report on the successful wafer-scale fabrication of actuator cantilevers and their characteristics. First test cantilevers show a cold-state deflection of 300 μm which, however, is limited by the silicon substrate. Upon heating, the cantilever shows a stroke of approx. 80 μm.