Special Session CJ-6
State-of-the-art Development and Application of Thin Film Piezoelectric MEMS/NEMS


Session CJ-6.1 - New Piezomaterials Systems, Film Growth, Multilayers, Heterostructures, Characterisation

CJ-6.1:IL01  Giant Piezoelectricity on Si for Hyperactive MEMS
SEUNG-HYUB BAEK1,2, J. PARK3, D.M. KIM2, V.A. AKSYUK4, R.R. DAS2, S.D. BU2, D.A. FELKER5, J. LETTIERI6, V. VAITHYANATHAN6, S.S.N. BHARADWAJA6, N. BASSIRI-GHARB6, Y.B. CHEN7, H.P. SUN7, C.M. FOLKMAN2, H.W. JANG2, D.J. KREFT3, S.K. STREIFFER8, R. RAMESH9, X.Q. PAN7, S. TROLIER-MCKINSTRY6, D.G. SCHLOM6,10, M.S. RZCHOWSKI4, R.H. BLICK3, C.B. EOM2, 1Electronic Materials Research Center, Korea Institute of Science and Technology, Seoul, Rep.of Korea; 2Dept. of Materials Science and Engineering, University of Wisconsin, Madison, WI, USA; 3Dept. of Electrical and Computer Engineering, University of Wisconsin, Madison, WI, USA; 4Center for Nanoscale Science and Technology, NIST, Gaithersburg, MD, USA; 5Dept. of Physics, University of Wisconsin, Madison, WI, USA; 6Dept. of Materials Science and Engineering, Penn State University, University Park, PA, USA; 7Dept. of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, USA; 8Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL, USA; 9Dept. of Materials Science and Engineering, University of California, Berkeley, CA, USA; 10Dept. of Materials Science and Engineering, Cornell University, Ithaca, NY, USA

Smart materials that can sense, manipulate, and position are crucial to the functionality of micro- and nano-machines. Integration of single crystal piezoelectric films on silicon offers the opportunity of high performance piezoelectric microelectromechanical systems (MEMS) incorporating all the advantages of large scale integration on silicon substrates with on-board electronic circuits, improving performance and eliminating common failure points associated with heterogeneous integration. We have fabricated oxide heterostructures with the highest piezoelectric coefficients (e31= -27 ± 3 C/m2) and figure of merit for piezoelectric energy harvesting system ever realized on silicon substrates by synthesizing epitaxial thin films of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) on vicinal (001) Si wafers using an epitaxial (001) SrTiO3 template layer. We have also demonstrated fabrication of PMN-PT cantilevers, whose mechanical behavior is consistent with theoretical calculations using the material constants of a bulk PMN-PT single crystal. These epitaxial heterostructures with giant piezoelectricity can be used for Micro and Nano Electro Mechanical Systems (MEMS and NEMS) that function with low drive voltage such as transducers for ultrasound medical imaging and micro-fluidic control.

CJ-6.1:IL04  Strain and Substrate Clamping Dependence of Piezoelectric Properties of Epitaxial PMN-PT Relaxor Ferroelectric Thin Films
CHANG-BEOM EOM, Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, USA

We have previously demonstrated giant piezoelectricity in single-crystal epitaxial bulk single crystal relaxor ferroelectric Pb(Mg1/3Nb2/3)-PbTiO3 (PMN-PT) thin films with the highest piezoelectric coefficients and figures of merit for piezoelectric energy harvesting systems ever realized on silicon substrates [1].  Enormous epitaxial and thermal strains can exist in thin films due to differences in lattice parameters and thermal expansion behavior between the film and the underlying substrate or arising from defects formed during film deposition.  As a result, the properties of thin films can be dramatically different from the intrinsic properties of the corresponding unstrained bulk materials.  While such strain often leads to degraded film properties, if judicious use is made of substrates and growth parameters, strain offers the opportunity to enhance particular properties of a chosen material in thin film form, namely strain engineering [2].  We have investigated the piezoelectric properties of relaxor ferroelectric PMN-PT thin films grown on a variety of substrates with different lattice parameters.  These substrates are highly compatible with perovskites such as PMN-PT due to their similar structures and chemical and thermal properties.  This compatibility facilitates the growth of high-quality films with enhanced properties. We will discuss the symmetry, three-dimensional strain states and domain structures, and piezoelectric properties of the PMN-PT thin films determined by four-circle x-ray diffraction and piezo-force microscopy.  We will also discuss the strain and substrate clamping dependence of the piezoelectric properties, and the phase diagram of the PMN-PT thin films using phase-field simulations. 
[1]. S.H. Baek et al., Science, 334, 958 (2011)
[2] K. J. Choi et al., Science, 306, 1005 (2004)
This work has been done in collaboration with A. Frey, A. K.H. Cho, J. Frederick, L. Hong, L.Q. Chen, M.S. Rzchowski and C.B. Eom

CJ-6.1:L06  Piezoelectric AlN Thin Films on Kapton
F. GUIDO, M. DE VITTORIO, Center for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia, Arnesano (LE), Italy and Dip. Ingegneria dell'Innovazione of Università del Salento, Lecce, Italy; M.T. TODARO, National Nanotechnology Laboratory Istituto Nanoscienze - CNR, Lecce, Italy; V. MASTRONARDI, Dip. Scienza Applicata e Tecnologia, Torino, Italy; S. PETRONI, Center for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia, Arnesano (LE), Italy

Piezoelectric materials on polymers are interesting for their ability to generate a voltage under mechanical stress and to strain by applying an electric field; this ability is augmented when the substrate is flexible because higher strains are possible. In this prospect an interesting material system is Aluminum Nitride (AlN) on flexible substrate. AlN has a moderate piezoelectric coefficient (d33 =4-5pm/V) and very good electric properties. Moreover it can be easily integrated on polymers by low temperature sputtering, enhancing significantly the piezoelectric response. In this work we study the reactive sputtering deposition by DC pulsed mode of AlN on Kapton analyzing the fundamental growth parameters: pulse frequency, pressure, power, impact on c-axis orientation, piezoelectric coefficient and residual stress. C-axis orientation is studied by the FWHM of rocking curve obtained with X-Ray diffraction spectra, the piezoelectric coefficient d33 is measured by exciting the thickness mode and measuring the out of plane displacement with a Laser Doppler Vibrometer. We show that a fast and efficient method to estimate the residual stress of the material in small areas is the measurement of the curvature of the AlN layer patterned in sub-millimeter sized dome shapes by profilometry.

Session CJ-6.2 - Microfabrication, Device Design

CJ-6.2:IL02  Screen-printed Ceramic Based MEMS Piezoelectric Cantilever for Harvesting Energy
SWEE LEONG KOK, A.R. OTHMAN, Faculty of Electronic and Computer Engineering, Universiti Teknikal Malaysia Melaka, Melaka, Malaysia; A. SHAABAN, Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka, Melaka, Malaysia

Screen-printing technology provides a convenient method in fabricating thick-film conductive circuits and devices in the past few decades. Recently with the introduction of high performance piezoelectric material such as lead zirconate titanate (PZT), has created new interest in ceramic based MEMS energy harvesting devices. Generally, the piezoelectric cantilever is used to operate in bending mode to generate maximum electrical charges when vibrated to its resonance frequency. As the charges generation is proportional to the mechanical stress on the material, therefore the constraint on the material should reduce to minimum. In this paper, a series of piezoelectric cantilevers is being designed and fabricated with the bending operating part free from substrate in a free-standing form. The electrical and mechanical properties of the thick-film devices were characterized and the piezoelectric charges coefficient of 80 pCN-1 was measured for a sample with thickness of about 50 um and co-fired at temperate 950 C. An electrical output power of 110 uW and an open-circuit voltage of about 5.8 V were measured when the free-standing structure with a proof mass of 0.38 g attached to the tip of the cantilever, was excited to its resonant frequency of 155 Hz at an acceleration of 6 g-level.

CJ-6.2:IL04  Nanoscale Domains in Ferroelectric PbTiO3 Films and PbTiO3/SrTiO3 Superlattices
P. ZUBKO, University College London, London Centre for Nanotechnology, London, UK; S. FERNANDEZ, C. LICHTENSTEIGER, J.-M. TRISCONE, University of Geneva, Geneva, Switzerland

Ferroelectric superlattices consisting of alternating ultrathin layers of ferroelectric and non-ferroelectric oxides have been the subject of numerous studies aimed at both the fundamental understanding of ferroelectricity in the ultrathin limit, and at designing artificial ferroelectrics with tailored functional properties. Epitaxial strain and electrostatic interaction between the ferroelectric layers both play a crucial role in determining the structure and domain formation that underlie most of the functional characteristics of these heterostructures. Using a combination of high-resolution transmission electron microscopy, dielectric measurements and X-ray diffraction with in-situ applied electric fields, we have studied the structure and dynamics of depolarisation-field-induced ferroelectric nanodomains and their effect on the dielectric and piezoelectric properties of PbTiO3-SrTiO3 superlattices. The nanodomains have been linked with highly inhomogeneous internal polarization and strain distributions within the superlattices and were found to contribute to a large enhancement of the dielectric response. Direct real space imaging of nanodomains in PbTiO3 thin films was also performed using piezoelectric force microscopy.

CJ-6.2:IL05  SINTEF PiezoMEMS Competence Centre
F. TYHOLDT, A. VOGL, H. TOFTEBERG, N.P. OESTBOE, T. BAKKE, F. LAPIQUE, SINTEF, Microsystems and Nanotechnology, Oslo, Norway

Since piezoMEMS technology is industrially a quite new technology it is natural that the barrier for considering piezoMEMS technology can be high. The piezoMEMS Competence Centre at SINTEF (www.piezomicrosystems.com) is a perfect match for small and medium size fabless companies that want to get started with piezoMEMS or larger companies that needs access to piezoMEMS processing competence. The competence centre has experience with making piezoMEMS devices since 2002 and covers the whole production process from design, through materials development and device fabrication to packaging. A key to piezoMEMS is to both have deep material and MEMS competence. The competence centre aims to have agreements with MEMS fabs for more straightforward transfer to high volume production after the prototyping stage.
A key goal of SINTEF is to develop new piezoMEMS concepts both internally and together with our customers. Several successful projects have been completed and results from the fabricated piezoMEMS devices will be presented. We also want to present the status of the competence centre in terms of equipment and processes as well as our new automated PLD and CSD tools for deposition of PZT on up to 200 mm wafers.

CJ-6.2:IL06  The PiezoElectronic Switch: a Path to High Speed, Low Energy Electronics
D.M. NEWNS, P.M. SOLOMON, B. BRYCE, T.M. SHAW, M. COPEL, L-W. HUNG, A. SCHROTT, T.N.THEIS, W. HAENSCH, S.M. ROSSNAGEL, H. MIYAZOE, B.G. ELMEGREEN, M.A. KURODA, X-H. LIU, G.J. MARTYNA, IBM T.J. Watson Research Center, Yorktown Hgts., NY, USA; S. TROLIER-MCKINSTRY, R. KEECH, S. SHETTY, Department of Material Science and Engineering, Penn State University, College Park, PA, USA

The information age has produced astonishing improvements in compute power, but the current highly successful CMOS technology is running into power limitations. A fundamentally new device concept is needed in order to take computing into a new lower power regime. In the approach described here [1],[2] the gate input is applied across a Piezoelectric (PE) actuator, which expands and compresses an adjacent Piezoresistor (PR). The PR, a material which undergoes a pressure-driven semiconductor-metal transition, then conducts, turning the switch on. Simulation and modeling, based on the properties of known materials, shows that the device, the PiezoElectronic switch (PET), is capable of forming the switching element in a CMOS-analog logic, functioning at higher speeds than current CMOS but at 1/100 the power. We describe the fabrication and results of the two forms of device which have been fabricated so far, and outline the future trajectory of the technology.
[1] D.M. Newns et al. "A Low-Voltage High-Speed Electronic Switch based on Piezoelectric Transduction," J. Appl. Phys. Vol. 111, 084509, (2012).
[2] M. Copel et al., "Giant Piezoresistive On/Off Ratios in Rare-Earth Chalcogenide Thin Films Enabling Nanomechanical Switching," Nanoletters, in press.

Session CJ-6.3 - Thin Film Piezoelectric MEMS/NEMS Applications

CJ-6.3:IL01  Applications of Piezoceramic Thick Films
E. RINGGAARD, T. ZAWADA, K. ASTAFIEV, M. GUIZZETTI, L.M. BORREGAARD, R. XU, K. ELKJAER, W.W. WOLNY, Meggitt Sensing Systems, Kvistgaard, Denmark

Piezoceramic thick films is a very promising technology in view of the challenges imposed by the trends in piezoelectric applications towards miniaturisation, integration and higher frequencies. The thick films described here (thickness 20 to 80 µm) are manufactured by screen printing or pad printing, which are suitable techniques for up-scaling and for patterning according to the design needed. Therefore they offer attractive solutions in those cases where machining of bulk ceramics is too difficult, while a larger active volume is needed than what is realistically obtainable with thin films.
The conventional thick films can be deposited on a variety of substrates that can be processed at temperatures of 850 ºC and above, e.g. silicon, and both lead zirconate titanate (PZT) and potassium sodium niobate (KNN) films have been realised. However, certain applications require the films to be deposited on polymers or other low-temperature substrates and for this purpose PiezoPaint(TM) has been developed. This is a composite of PZT and a suitable polymer and has piezoelectric properties superior to those of piezoelectric polymers. Examples of thick-film applications will be given, including energy harvesting, high-frequency ultrasonic imaging, sensors and structural health monitoring.

CJ-6.3:IL02  AlN Thin Films for Resonators Applications

Four different applications involving AlN thin films resonators will be addressed in this talk. Bulk acoustic waves resonators in the GHz range are the main components for RF duplexers. They are made of AlN films with dedicated electrodes and an insulating acoustic Bragg mirror or a cavity. In this configuration, AlN is very well coupled (7% electromechanical coupling kt²) and the quality factor Q of the resonator can reach values as high as 2000. For Lamb wave devices, one addresses a larger frequency range from 100MHz to several GHz with in-plane designs. The coupling is smaller (typ. 2%) but Q can reach 3000. This is the preferred structure to perform phononic crystals out of thin films. AlN gives also the opportunity to obtain ultra high Q resonators with the highest Q x f product known for acoustic resonators, namely 1.1 e14 Hz. The configuration used to obtain such a high value is called HBAR where AlN thin films are combined with high Q acoustic substrates as sapphire. This can be very useful for ultra-stable oscillators. Finally AlN ultra thin films (<50nm) can be integrated into cantilevers to perform ultimate mass measurements device for gas detection. These four aspects will be detailed through experimental devices realized at CEA LETI.

CJ-6.3:L03  Micropump with Active Valves Based on Thin Film PZT

We present a micropump with integrated active valves actuated by thin film PZT. The active valves, which can also be used as stand-alone elements, make bi-directional pumping of both gases and liquids possible with good flow control.
To our knowledge this is the first micropump with active valves based on thin film PZT. Accurate control of small volumes of gases and liquids is required in medical applications, fuel cells, printers and gas sensors. Our pump has been designed as an insulin pump with an area of 8x8 mm and < 1 mm thickness.
The pump and valves work by deformation of membranes connected to a centered piston. The design was realized on a silicon-on-insulator (SOI) wafer. The circular pumping piston was formed in the handle wafer of the SOI. The 2 µm thick PZT was deposited using chemical solution deposition (CSD). The SOI wafer was bonded to a fill wafer to minimize the dead volume inside the pump. The fill wafer was an SOI wafer where 90% of the 380 µm thick device layer had been removed by DRIE.
Polarization fatigue measurements showed less than 5% variation after 10^9 cycles at 10 MHz and 15 V. The stroke height was ± 8 µm. Design, process, electrical measurements and initial functional tests will be presented.

CJ-6.3:IL04  Performances of Ferroelectric Printed Films in Sensors and Energy Harvesting
V. FERRARI, Department of Information Engineering, University of Brescia, Italy

The use and performances of films based on lead zirconate titanate (PZT) ferroelectric ceramics deposited by screen printing and other techniques on different substrates, including alumina, steel and silicon, for sensors and energy conversion are reported.
In particular, based on the piezoelectric effect in the films, passive electromechanical resonant sensors with contactless interrogation for physical and chemical quantities, such as temperature, liquid properties, humidity or analytes in air, and energy harvesters from broadband vibrations based on multi-element arrays and nonlinear structures are experimentally demonstrated. Energy harvesting from thermal fluctuations exploiting the pyroelectric effect in the films is also reported.
A motivation of the presented research is the current trend in sensor development to increasingly aim at providing radio-frequency wireless signal transmission. Eliminating cables requires means to make energy available in the sensor unit for power supply. Passive sensors with energy supplied from an external interrogation module, and energy harvesting to power the sensor from the surroundings are attractive options. Either can be enabled by ferroelectric films embedded in miniaturized devices and MEMS.

CJ-6.3:IL05  Piezoelectric Micro-machined Ultrasonic Transducer for Medical Imaging
K. SMYTH, SANG-GOOK KIM, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA

Ultrasound is an attractive option for 3D and diagnostic medical imaging because it is relatively inexpensive, portable, compact, and non-invasive. MEMS transducer is the right technology that would enable 2D arrayed, small form factor ultrasound probes. Capacitive micromachined ultrasonic transducers (cMUTs) have recently been introduced as an alternative to existing bulk piezoelectric technology. However, cMUT's electrostatic actuation creates unavoidable drawbacks including the high DC bias voltage, non-linear behavior, small gap separation, and pull-in instability. Most importantly, acoustic power output is limited by the inevitable small gap height. The piezoelectric micro-machined ultrasonic transducer (pMUT) is a promising alternative to the cMUT. In this work, we present a unimorph pMUT design with electrode coverage optimized for large deflection and acoustic pressure output. We have focused on modeling and evaluation of pMUT performance through the device fabrication, formulating a more accurate analytical model and identifying useful performance metrics for optimal designs. By building on the shortcomings of existing models, we can now provide a wider range of tools for the designer to harness pMUT's full potential.

CJ-6.3:L06  2013-2018 Market Analysis of Thin Film Piezo MEMS
C. TROADEC, E. MOUNIER, Yole Développement, Lyon-Villeurbanne, France

Thin film piezoelectric materials are gaining more and more importance within the MEMS industry. Although semiconductor manufacturing companies are historically reluctant to introduce such exotic materials in their production lines, every major MEMS foundry nowadays is working on the implementation and qualification of piezoelectric thin film in their MEMS manufacturing processes.
First thin film piezoelectric MEMS applications are now on the market : in September 2013, EPSON has revealed the introduction of thin film PZT for their MEMS inkjet heads.
We have analyzed and estimated the MEMS/NEMS applications for piezoelectric thin films. We particularly looked at thin film PZT based applications : Ink Jet heads, Wafer Level Autofocus, micro-pumps, micro-mirrors, IR detectors, gyros, accelerometers, ultrasound medical imaging transducers, energy harvesting, optical switches.
Our talk will review the different applications, technological challenges and market volume of such thin film piezoelectric MEMS.

CJ-6.3:IL07  Comparison of Output Voltage and Power Generated from Tetragonal and MPB Composition PZT Thin Films Integrated on Piezoelectric Microcantilevers with Proof Mass
T. KOBAYASHI, Y. SUZUKI, N. MAKIMOTO, T. ITOH, R. MAEDA, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan; H. FUNAKUBO, Tokyo Institute of Technology, Tokyo Japan

Various piezoelectric MEMS (pMEMS) devices such as inkjet heads employ PZT thin films as actuators. Such devices utilize MPB-PZT for their high piezoelectric constant d31. We are exploring new application of pMEMS including activation switches, energy harvesters. For such application, the figure of merit d31/e and d31^2/e (e: dielectric constant) express the performance of output voltage and power generation, respectively. Theoretical calculation of d31/e and d31^2/e expects that tetra-PZT are more suitable than MPB-PZT for the activation switches and energy harvesters.
To date, several study have reported the influence of Zr/Ti on d31 and e of PZT thin films. However, few have reported an experimental comparison of the output voltage and power generation of tetra-PZT and MPB-PZT integrated into MEMS devices. Then, we have fabricated piezoelectric microcantilever with proof mass using tetra-PZT and MPB-PZT, and compared d31, output voltage, AC and DC power generation. The tetra-PZT have shown 3 times larger output voltage and 5 times larger power generation than MPB-PZT. The results indicated that a figure of merit d31/e is more important than d31 itself for the application to piezoelectric MEMS devices which transduce mechanical deformation into electrical output.

CJ-6.3:IL08  Piezoelectric Films for Next Generation Logic Elements
R. KEECH1, S. SHETTY1, S. TROLIER-MCKINSTRY1, D. NEWNS2, GLENN MARTYNA2, T. SHAW2, B. BRYCE2, M. COPEL2, 1Department of Material Science and Engineering, Pennsylvania State University University Park, PA, USA; 2IBM TJ Watson Research Center

A novel device architecture has been proposed for a replacement for Si-based CMOS electronics, which uses a piezoelectric actuator to trigger changes in the electrical resistivity of a piezoresistive element. In order for such a device to function, it is imperative to be able to maintain large piezoelectric constants at very small lateral length scales of the actuator (<< 1 μm). This paper will discuss the planned piezotronic elements, as well as approaches being taken to prepare {001} PbZr0.52Ti0.48O3 and PbMg1/3Nb2/3O3-PbTiO3 (PMN-PT) films and laterally patterning them. For aspect ratios of > 2:1 height:lateral feature sizes, reactive ion etching must be employed. Measurements on reactively ion etched structures demonstrate that the properties of the PMN-PT layers improve as the lateral feautures size is reduced. This paper will discuss the piezoelectric properties as a function of scale, as well as device performance for the piezoelectronic transistors.

CJ-6.3:IL09  Sc-doped Aluminum Nitride Thin Films for Energy Harvesting Applications
P. MURALT,  R. MATLOUB, A. MAZZALAI, Ceramics Laboratory, Ecole Polytechnique Fédérale de Lausanne, Switzerland; G. MOULARD, T. METZGER, EPCOS, Munich, Germany

AlN thin films have become a standard material for RF filters in mobile phones, exploiting the longitudinal piezoelectric effect. Recently it was shown that partial substituting of Al by Sc leads to a remarkable increase of this longitudinal effect. This opens new perspectives for wide band RF filters in the GHz range. For other MEMS applications, the transverse piezoelectric effect is more of interest, particularly for vibration energy harvesting in a resonant mode, re-quiring a good combination of piezoelectric coupling, low dielectric constant, and good quality factor. In this work, the transverse piezoelectric coefficient, e31,f , of Al1-xScxN thin films was in-vestigated as a function of composition. It increased nearly 50 % from x=0 to x=0.17. As the in-crease of the dielectric constant is only moderate we observed a more than 60 % increase of the electrical energy content to be harvested. The energy harvesting FOM of 18.0 (GJ/m3) for Al0.83Sc0.17N is comparable with good PZT thin films. We shall show that the harvesting efficiency is potentially increased by more than 60 % as compared to pure AlN. Going to even higher Sc concentrations, a doubling of the harvested power is conceivable. A review of all available data on this new material will be made.

Cimtec 2014

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