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10 pages, 25468 KiB

Open AccessArticle

Power Optimization of TiNiHf/Si Shape Memory Microactuators

by Gowtham Arivanandhan, Zixiong Li, Sabrina M. Curtis, Lisa Hanke, Eckhard Quandt and Manfred Kohl

Actuators 2023, 12(2), 82; https://doi.org/10.3390/act12020082 - 15 Feb 2023

Cited by 5 | Viewed by 2814

Abstract

We present a novel design approach for the power optimization of cantilever-based shape memory alloy (SMA)/Si bimorph microactuators as well as their microfabrication and in situ characterization. A major concern upon the miniaturization of SMA/Si bimorph microactuators in conventional double-beam cantilever designs is that direct Joule heating generates a large size-dependent temperature gradient along the length of the cantilevers, which significantly enhances the critical electrical power required to complete phase transformation. We demonstrate that this disadvantage can be mitigated by the finite element simulation-assisted design of additional folded beams in the perpendicular direction to the active cantilever beams, resulting in temperature homogenization. This approach is investigated for TiNiHf/Si microactuators with a film thickness ratio of 440 nm/2 µm, cantilever beam length of 75–100 µm and widths of 3–5 µm. Temperature-homogenized SMA/Si microactuators show a reduction in power consumption of up to 48% compared to the conventional double-beam cantilever design. Full article

(This article belongs to the Special Issue Cooperative Microactuator Systems)

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11 pages, 4194 KiB

Open AccessArticle

Bipolar Resistive Switching in Hafnium Oxide-Based Nanostructures with and without Nickel Nanoparticles

by Markus Otsus, Joonas Merisalu, Aivar Tarre, Anna-Liisa Peikolainen, Jekaterina Kozlova, Kaupo Kukli and Aile Tamm

Electronics 2022, 11(18), 2963; https://doi.org/10.3390/electronics11182963 - 19 Sep 2022

Cited by 4 | Viewed by 2234

Abstract

As research into additives and intentionally introduced impurities in dielectric thin film for enhancing the resistive switching based random access memories (RRAM) continues to gain momentum, the aim of the study was to evaluate the effects of chemically presynthesised Ni nanoparticles (NPs) embedded in a dielectric layer to the overall structure and resistive switching properties. HfO₂-based thin films embedded with Ni NPs were produced by atomic layer deposition (ALD) from tetrakis(ethylmethylamino)hafnium (TEMAH) and the O₂ plasma ALD process onto a TiN/Si substrate. The Ni NPs were separately synthesised through a continuous flow chemistry process and dispersed on the dielectric layer between the two stages of preparing the HfO₂ layer. The nanodevices’ morphology and composition were analysed with physical characterisation methods and were found to be uniformly dispersed across the sample, within an amorphous HfO₂ layer deposited around them. When comparing the resistive switching properties of otherwise identical samples with and without Ni NPs, the ILRS/IHRS ratio rose from around a 4 to 9 at 0.2 V reading voltage, the switching voltage dropped from ~2 V to ~1.5 V, and a distinct increase in the endurance characteristics could be seen with the addition of the nanoparticles. Full article

(This article belongs to the Section Circuit and Signal Processing)

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9 pages, 941 KiB

Open AccessProceeding Paper

Temperature Homogenization of Co-Integrated Shape Memory—Silicon Bimorph Actuators

by Gowtham Arivanandhan, Zixiong Li, Sabrina Curtis, Prasanth Velvaluri, Eckhard Quandt and Manfred Kohl

Proceedings 2020, 64(1), 8; https://doi.org/10.3390/IeCAT2020-08501 - 20 Nov 2020

Cited by 2 | Viewed by 2009

Abstract

The high work density and beneficial downscaling of shape memory alloy (SMA) actuation performance provide a basis for the development of actuators and systems at microscales. Here, we report a novel monolithic fabrication approach for the co-integration of SMA and Si microstructures to enable SMA-Si bimorph microactuation. Double-beam cantilevers are chosen for the actuator layout to enable electrothermal actuation by Joule heating. The SMA materials under investigation are NiMnGa and NiTi(Hf) films with tunable phase transformation temperatures. We show that Joule heating of the cantilevers generates increasing temperature gradients for decreasing cantilever size, which hampers actuation performance. In order to cope with this problem, a new method for design optimization is presented based on finite element modeling (FEM) simulations. We demonstrate that temperature homogenization can be achieved by the design of additional folded beams in the perpendicular direction to the active beam cantilevers. Thereby, power consumption can be reduced by more than 35 % and maximum deflection can be increased up to a factor of 2 depending on the cantilever geometry. Full article

(This article belongs to the Proceedings of The 1st International Electronic Conference on Actuator Technology: Materials, Devices and Applications)

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12 pages, 5092 KiB

Open AccessArticle

Phonon Bridge Effect in Superlattices of Thermoelectric TiNiSn/HfNiSn With Controlled Interface Intermixing

by Sven Heinz, Emigdio Chavez Angel, Maximilian Trapp, Hans-Joachim Kleebe and Gerhard Jakob

Nanomaterials 2020, 10(6), 1239; https://doi.org/10.3390/nano10061239 - 25 Jun 2020

Cited by 2 | Viewed by 3621

Abstract

The implementation of thermal barriers in thermoelectric materials improves their power conversion rates effectively. For this purpose, material boundaries are utilized and manipulated to affect phonon transmissivity. Specifically, interface intermixing and topography represents a useful but complex parameter for thermal transport modification. This study investigates epitaxial thin film multilayers, so called superlattices (SL), of TiNiSn/HfNiSn, both with pristine and purposefully deteriorated interfaces. High-resolution transmission electron microscopy and X-ray diffractometry are used to characterize their structural properties in detail. A differential 3

ω

-method probes their thermal resistivity. The thermal resistivity reaches a maximum for an intermediate interface quality and decreases again for higher boundary layer intermixing. For boundaries with the lowest interface quality, the interface thermal resistance is reduced by 23% compared to a pristine SL. While an uptake of diffuse scattering likely explains the initial deterioration of thermal transport, we propose a phonon bridge interpretation for the lowered thermal resistivity of the interfaces beyond a critical intermixing. In this picture, the locally reduced acoustic contrast of the less defined boundary acts as a mediator that promotes phonon transition. Full article

(This article belongs to the Special Issue Thermal Transport in Nanostructures and Nanomaterials)

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