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NiTi thin films with robust shape memory effects and low deposition temperatures are greatly desired for microelectronic devices. However, sub-micron films deposited below 425 °C usually have amorphous structure and must be post-annealed to achieve full crystallization. In this article, using Ru as a seed layer, we demonstrate growth of NiTi films as thin as 120 nm with in-situ crystallization at 325 °C. NiTi thin films with a wide range of growth parameters including deposition temperature and film thickness were investigated. Shape memory effects were characterized using stress bow and resistivity studies. Structural information across the R-phase to austenite transformation was obtained using X-ray diffraction. NiTi thin films exhibited a narrow hysteresis during R-phase to austenite phase transition near 60 °C while possessing good shape memory properties.

NiTi SMA thermal bimorph actuators have potential as high-force, high-displacement MEMS actuators. Historically, even microscale SMA actuation response has been limited to a maximum of ˜100 Hz. As NiTi film and device dimensions are scaled down into the micro and nano scales, heat transfer, and thus device cycling speeds can be significantly improved upon. We have used an in-situ annealed nickel-titanium (NiTi) shape memory alloy (SMA) sputter deposition process to sputter equiatomic NiTi films at 600 °C. We characterized our thin film (270 nm NiTi – 1.6 μm NiTi) material and verified its reversible shape memory effects (SME) using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and wafer bow versus temperature measurements. Upon release, the NiTi material exhibited a reversible phase change around 60 °C with a hysteresis of ˜3 °C. For the substrate confined case (i.e. NiTi on Si or Pt), hysteresis was much larger (i.e. ˜40 °C) with the phase change completed at ˜80 °C. In addition to SMA material characterization, we fabricated NiTi/Pt bimorph actuators at several (100 nm to 1.2 μm) NiTi and Pt thicknesses. Free-standing bimorph actuators were produced via a dry etch release, and temperature dependent curvature of these cantilevers was investigated. To address the low power, and high response time aspects, we performed a dynamic characterization using a 440 mW, 532 nm “green” laser to irradiate devices from 2 to 24 W/cm2 while measuring actuation response times that varied from 3 ms at the highest irradiation fluxes to 240 ms at the lowest. Our results showed decreased actuation powers and faster heating or actuation times compared to past works with NiTi microactuators. The NiTi films with 600 nm thickness on top of 20 nm Pt films exhibited the greatest change in curvature from 200 μm to flat states, and actuated in under 3 ms due to the very small volume of SMA requiring to be heated. These results suggest that NiTi/Pt bimorphs have potential applications as lower-power, faster-response, laser-activated micro shutters or thermal switches without needing a traditional wired power source.

Combining electrical and magnetic materials in the same part has been a challenge in 3D printing due to difficulties co-printing complex materials in many additive manufacturing processes. Past 3D printed inductors and other similar magnetic devices have therefore either lacked the magnetic materials necessary for improved performance, or required sintering at high temperatures for extended periods, beyond the capability of most 3D printable polymers. In this work, we demonstrate a room temperature process for incorporating conductive and magnetic materials into the same 3D printed device. A multi-stage fabrication process based on 3D printing followed by fill with magnetic and conductive fluids is proposed. Multi-layer microfluidic channels for magnetic passives are first printed in a stereolithography process. The microfluidic systems are then filled with room temperature liquid metal, a gallium alloy liquid at room temperature, and ferrofluid to create inductors, transformers and wireless power coils. Through the addition of ferrofluid as a magnetic material, increases in inductance density by nearly a factor of three were demonstrated, in addition to coupling improvements for transformer and wireless power coils compared to the devices before magnetic fill.

Origami-inspired folding is a well-established method for creating 3D shapes from two dimensional sheets. Here we demonstrate for the first time using a laser to fold, assemble and propel the resulting free-moving part, all without any need for handling. Being able to remotely assemble and move complex parts is an important manufacturing innovation, with potential for controlling doors and latches as well as launching parts off of the build platform without direct assistance. Beginning with only a blank sheet of metal, the parts are first cut and folded using laser forming, where a laser is used to create localized plastic stresses to bend the workpiece. After dropping into place with a final cut, the resulting rotor is actuated with laser ablation propulsion, using a jet of ablated material to apply thrust.

Fused filament fabrication (FFF) 3D printers have been largely limited to thermoplastics in the past but with new composite materials available on the market there are new possibilities for what these machines can produce. Using a conductive composite filament, electronic components can be manufactured but due to the filament’s relatively poor electrical properties, the resulting traces are typically highly resistive. Selective electroplating on these parts is one approach to incorporate materials with high conductivity onto 3D-printed structures. In this paper, non-conductive and conductive filaments printed in the same part are used to enable selective electroplating directly on regions defined by the conductive filament to create metallic parts through 3D printing. This technique is demonstrated for the creation of multiple distinct conductive segments and to electroplate the same part with multiple metals to, for instance, allow a magnetic metal such as nickel and a highly conductive one such as copper to be incorporated in the same part. Following the characterization of the process, a representative 3D printed electrical device, a selectively electroplated solenoid inductor with low frequency inductance and resistance of 191 nH and 18.7 mΩ respectively was manufactured using this technique. This is a five order of magnitude reduction in resistance over the original value of 3 kΩ for the inductor before electroplating.

When infused with an oxidizer, on-chip porous silicon (PS) shows tremendous potential as an energetic material. However, applications such as fuzing and propulsion require long-term material stability. The present work utilizes accelerated lifetime testing for PS samples with sodium perchlorate (NaClO4) oxidizer. Devices were exposed to elevated temperatures for various time intervals, then subjected to an electrical pulse through an integrated bridgewire to test for ignition. The pass/fail data from ignition testing was then analyzed to determine the mean and median failure point at each temperature using an Arrhenius aging model and a lognormal probability density function (PDF). Samples were heated over a temperature range of 185–300 °C for up to 46 h with median failure times ranging from 0.4–20 h. Differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were used to evaluate chemical changes of PS/NaClO4 during aging. Comparison of DSC traces for aged samples showed differences for heating above and below 250 °C, suggesting two different aging mechanisms. FTIR results suggest that for low temperature aging (below ∼250 °C) the hydrogen termination layer of the porous silicon was still intact, but backbond oxidation did occur. Above ∼250 °C the hydrogen termination layer was no longer evident in FTIR and considerable oxidation occurred, suggesting reaction or dissociation of the hydrogen layer. This corresponds with an exothermic peak shown during DSC at 300 °C. Thermogravimetric analysis/mass spectroscopy (TGA/MS) was also performed, and confirmed hydrogen gas release beginning at ∼280 °C. A DSC peak at ∼400 °C is evident for fresh samples, but is greatly reduced or not evident for all aged samples. We attribute this peak to backbond oxidation, which is shown to occur in FTIR for all aged samples. Variable heating rate DSC experiments were also performed to determine activation energy of fresh and aged samples. Activation energy was calculated using the Kissinger Method for the first two exothermic peaks in DSC experiments. For the first peak, corresponding to hydrogen desorption (∼300 °C), activation energy for fresh and aged samples was 132.1 kJ/mol and 132.7 kJ/mol, respectively. The activation energy of the second exothermic peak, corresponding to backbond oxidation, for fresh and aged samples was 183.8 kJ/mol and 159.6 kJ/mol, respectively. Device failure during accelerated aging tests was also used to predict the mean lifetime of porous silicon/sodium perchlorate at room temperature (25 oC) as 100 years with a 90% confidence interval of 31 to 328 years.

We describe the design, modeling, fabrication, and testing of a MEMS inertial switch that can detect accelerations in the x, y, and z axes using a single mass/spring assembly (first reported in Ref. [1] ). A spiral spring suspension is used which is compliant in all directions. The inertial switch approach offers zero power draw until an acceleration event occurs. Arrays of individual triaxial sensors are created on a single chip, with each switch designed to close at a different acceleration threshold between 50 g and 250 g. A resistor ladder connects each switch together in series such that the number of pinouts from the chip is substantially reduced. The response of the switch array to half-sine acceleration pulses of 5–8 ms duration is reported, with multiple switches in the array closing and opening in sequence for higher magnitude acceleration pulses. The switch closure time under these conditions is consistently less than 200 μs, and bounce is minimal for applied accelerations lower than 200 g.

An integrated approach to the fabrication of thin-film piezoelectric traveling wave ultrasonic motors at the mm-scale is being developed for low power, high torque motors for small scale robotics, biomedical, and sensing applications. This paper describes the realization of ultrasonic motor stators ranging in diameter from 1 to 3 mm using wafer scale MEMS fabrication techniques with lead zirconate titanate (PZT) thin films. Using laser Doppler vibrometry (LDV), controlled traveling waves were demonstrated in the bulk silicon elastic medium of the stator and the standing wave behavior was characterized for control purposes. Furthermore, the resonant modes of the fabricated stators were modeled using finite element models, and experimental results agree well with this analysis.