Major challenges have emerged as microelectromechanical systems (MEMS) move to smaller size and increased integration density, while requiring fast response and large motions. Continued scaling to nanoelectromechanical systems (NEMS) requires revolutionary advances in actuators, sensors, and transducers. MEMS and NEMS utilizing piezoelectric thin films provide the required large linear forces with fast actuation at small drive voltages. This, in turn, provides accurate displacements at high integration densities, reduces the voltage burden on the integrated control electronics, and decreases NEMS complexity. These advances are enabled by the rapidly growing field of thin-film piezoelectric MEMS, from the development of AlN films for resonator and filter applications, to their implementation in adaptive radio front ends, to the demonstration of large piezoelectricity in epitaxial Pb(Zr,Ti)O3 and PbMg1/3Nb2/3O3–PbTiO3thin films. Applications of low voltage MEMS/NEMS include transducers for ultrasound medical imaging, robotic insects, inkjet printing, mechanically based logic, and energy harvesting. As described in this article, advances in the field are being driven by and are prompting advances in heterostructure design and theoretical investigations.

Microelectromechanical systems (MEMS) incorporating piezoelectric layers provide active transduction between electrical and mechanical energy, which enables highly sensitive sensors and low-voltage driven actuators surpassing the passive operation of electrostatic MEMS. Several different piezoelectric materials have been successfully integrated into MEMS structures, most notably Pb(Zr,Ti)O3. Piezoelectric materials with larger piezoelectric response, such as the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3(PMN-PT), would enable further miniaturization. However, this has long been hampered by the difficulties in the synthesis of these materials. This article reviews recent successes not only in synthesizing high-quality epitaxial PMN-PT heterostructures on Si, but also in fabricating PMN-PT microcantilevers, which retain the piezoelectric properties of bulk PMN-PT single crystals. These epitaxial heterostructures provide a platform to build MEMS and nanoelectromechanical system devices that function with large displacement at low drive voltages, such as ultrasound medical imagers, micro-fluidic control, piezotronics, and energy harvesting.

Films of piezoelectric and ferroelectric oxides have been widely investigated for various applications, including microelectromechanical systems (MEMS) for printing. Pb(Zr,Ti)O3 is of particular interest due to its excellent piezoelectric properties. Control of the density, crystalline orientation, and compositional uniformity is essential to obtain these properties. In this article, we review recent progress on the fabrication of epitaxial Pb(Zr,Ti)O3films, in which the aforementioned control can be achieved. We discuss the different approaches used for the deposition of the epitaxial piezoelectric layer as well as the achieved degrees of the epitaxy. Furthermore, the integration of these piezoelectric layers in MEMS and the corresponding performance are discussed.

Piezoelectric microelectromechanical systems (MEMS) have been proven to be an attractive technology for harvesting small magnitudes of energy from ambient vibrations. This technology promises to eliminate the need for replacing chemical batteries or complex wiring in microsensors/microsystems, moving us closer toward battery-less autonomous sensors systems and networks. To achieve this goal, a fully assembled energy harvester the size of a US quarter dollar coin (diameter = 24.26 mm, thickness = 1.75 mm) should be able to robustly generate about 100 μW of continuous power from ambient vibrations. In addition, the cost of the device should be sufficiently low for mass scale deployment. At the present time, most of the devices reported in the literature do not meet these requirements. This article reviews the current state of the art with respect to the key challenges such as high power density and wide bandwidth of operation. This article also describes improvements in piezoelectric materials and resonator structure design, which are believed to be the solutions to these challenges. Epitaxial growth and grain texturing of piezoelectric materials is being developed to achieve much higher energy conversion efficiency. For embedded medical systems, lead-free piezoelectric thin films are being developed, and MEMS processes for these new classes of materials are being investigated. Nonlinear resonating beams for wide bandwidth resonance are also being developed to enable more robust operation of energy harvesters.

This article reports on the state-of-the-art of the development of aluminum nitride (AlN) thin-film microelectromechanical systems (MEMS) with particular emphasis on acoustic devices for radio frequency (RF) signal processing. Examples of resonant devices are reviewed to highlight the capabilities of AlN as an integrated circuit compatible material for the implementation of RF filters and oscillators. The commercial success of thin-film bulk acoustic resonators is presented to show how AlN has de facto become an industrial standard for the synthesis of high performance duplexers. The article also reports on the development of a new class of AlN acoustic resonators that are directly integrated with circuits and enable a new generation of reconfigurable narrowband filters and oscillators. Research efforts related to the deposition of doped AlN films and the scaling of sputtered AlN films into the nano realm are also provided as examples of possible future material developments that could expand the range of applicability of AlN MEMS.

Thin-film piezoelectric lead zirconate titanate (PZT) is one of the most efficient electromechanical coupling transducer materials currently available for microelectromechanical systems (MEMS). This article reviews piezoelectric MEMS (piezo MEMS) technologies using PZT thin films in radio frequency (RF) devices for communications and radar applications and in the emerging field of millimeter-scale robotics. The electromechanical material properties of thin-film PZT uniquely enable insect-inspired and insect-scale autonomous robots. Recent progress on large force and displacement actuators for robotic leg joints, compact and high torque ultrasonic motors, and bioinspired millimeter-scale flapping wing platforms will be presented. The use of thin-film PZT to achieve high performance and low-voltage RF MEMS switches, ultralow power consumption nanomechanical logic circuits, and high coupling and low loss resonators, filters, and transformers are also reviewed.

Moore’s law of transistor scaling, the exponential increase in the number of complementary metal oxide semiconductor (CMOS) transistors per unit area, continues unabated; however, computer clock speeds have remained frozen since 2003. The development of a new digital switch, the piezoelectronic transistor (PET), is designed to circumvent the speed and power limitations of the CMOS transistor. The PET operates on a novel principle: an electrical input is transduced into an acoustic pulse by a piezoelectric element which, in turn, is used to drive a continuous insulator-to-metal transition in a piezoresistive element, thus switching on the device. Performance is enabled by the use of key high response materials, a relaxor piezoelectric, and a rare-earth chalcogenide piezoresistor. Theory and simulation predict, using bulk material properties, that PETs can operate at one-tenth the present voltage of CMOS technology and consuming 100 times less power while running at multi-GHz clock speeds. A program to fabricate prototype PET devices is under way.

The regime of mesoscale science, where the granularity of atoms and quantization of energy gives way to apparently continuous and infinitely divisible matter and energy, yields strikingly complex architectures, phenomena, and functionalities that control macroscopic material behavior. Research in mesoscale materials and chemical science is an opportunity space for next-generation discovery, science, technology, and innovation, with promise of new solutions for societal problems such as energy, environment, climate, advanced manufacturing, and economic growth.