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Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and...
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Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D：Materials and Processing".

Deadline for manuscript submissions: closed (19 June 2022) | Viewed by 39146

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editor

Dr. Agnė Žukauskaitė

E-Mail Website
Guest Editor
1. Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, 01277 Dresden, Germany
2. Institute of Solid State Electronics (IFE), the Faculty of Electrical and Computer Engineering, TU Dresden, 01062 Dresden, Germany
Interests: material science; physical vapor deposition; magnetron sputter epitaxy; III-nitrides; thin films; piezoelectric AlN and AlScN; electroacoustic applications

Special Issue Information

Dear Colleagues,

Not so long ago, aluminium scandium nitride (AlScN) emerged as a material that possesses superior properties as compared to aluminium nitride (AlN). Substituting Al by Sc in AlN leads to a dramatic increase in piezoelectric coefficient as well as electromechanical coupling. This discovery finally allowed us to overcome the limitations of AlN thin films in various piezoelectric applications while still benefiting from all the advantages of the parent material system, such as high temperature stability, CMOS compatibility, and good mechanical properties.

AlScN allows for enhanced performance of RF filters where bulk acoustic wave (BAW), or surface acoustic wave (SAW) resonators are used. Additionally, energy harvesting and sensing applications can benefit as well. Higher pyroelectric coefficients allow new advances in, for example, infra-red (IR) detectors. Recent progress in growing this material by MOCVD and MBE has opened new prospects in high-frequency and -power electronics, such as high electron mobility transistors (HEMTs). Finally, AlScN is the first wurtzite III-nitride where ferroelectric switching was observed a few years ago, opening another exiting research field with many possible applications in semiconductor memories as well as additional switching functionality to applications where piezoelectric materials are already in use.

We invite all researchers working with this exciting and versatile material to join our Special Issue fully focused on AlScN. Let us work together and finally provide the scientific community with a highly visible, multidisciplinary open access collection of recent advances in understanding the material itself as well as unlocking its full potential in microdevices.

The Special Issue seeks contributions addressing:

  • Fundamentals, physics, theory, and modeling of AlScN: material and devices
  • Growth and characterization of AlScN thin films
  • Design, fabrication, and performance of AlScN microdevices
  • Novel and niche applications for AlScN

Dr. Agnė Žukauskaitė
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • aluminium scandium nitride
  • piezoelectric thin films
  • ferroelectric switching
  • transducers and actuators
  • microfabrication
  • piezoelectric microdevices
  • MEMS

Published Papers (14 papers)

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Editorial

Jump to: Research

4 pages, 208 KiB  
Editorial
Editorial for Special Issue “Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices”
by Agnė Žukauskaitė
Micromachines 2023, 14(5), 1067; https://0-doi-org.brum.beds.ac.uk/10.3390/mi14051067 - 18 May 2023
Cited by 1 | Viewed by 1730
Abstract
The enhanced piezoelectric properties of aluminum scandium nitride (Al1−xScxN or AlScN) were discovered in 2009 by Morito Akiyama’s team [...] Full article
(This article belongs to the Special Issue Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices)

Research

Jump to: Editorial

13 pages, 2755 KiB  
Article
Raman Spectroscopy and Spectral Signatures of AlScN/Al2O3
by Dmytro Solonenko, Agnė Žukauskaitė, Julian Pilz, Mohssen Moridi and Sarah Risquez
Micromachines 2022, 13(11), 1961; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13111961 - 11 Nov 2022
Cited by 6 | Viewed by 2865
Abstract
III-V solid solutions are sensitive to growth conditions due to their stochastic nature. The highly crystalline thin films require a profound understanding of the material properties and reliable means of their determination. In this work, we have investigated the Raman spectral fingerprint of [...] Read more.
III-V solid solutions are sensitive to growth conditions due to their stochastic nature. The highly crystalline thin films require a profound understanding of the material properties and reliable means of their determination. In this work, we have investigated the Raman spectral fingerprint of Al1−xScxN thin films with Sc concentrations x = 0, 0.14, 0.17, 0.23, 0.32, and 0.41, grown on Al2O3(0001) substrates. The spectra show softening and broadening of the modes related to the dominant wurtzite phase with increasing Sc content, in agreement with the corresponding XRD results. We investigated the primary scattering mechanism responsible for the immense modes’ linewidths by comparing the average grain sizes to the phonon correlation length, indicating that alloying augments the point defect density. The low-frequency Raman bands were attributed to the confined spherical acoustic modes in the co-forming ScN nanoparticles. Temperature-dependent Raman measurements enabled the temperature coefficient of the E2(high) mode to be determined for all Sc concentrations for the precise temperature monitoring in AlScN-based devices. Full article
(This article belongs to the Special Issue Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices)
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17 pages, 2532 KiB  
Article
Laser Ultrasound Investigations of AlScN(0001) and AlScN(11-20) Thin Films Prepared by Magnetron Sputter Epitaxy on Sapphire Substrates
by Elena A. Mayer, Olga Rogall, Anli Ding, Akash Nair, Agnė Žukauskaitė, Pavel D. Pupyrev, Alexey M. Lomonosov and Andreas P. Mayer
Micromachines 2022, 13(10), 1698; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13101698 - 09 Oct 2022
Cited by 2 | Viewed by 1690
Abstract
The laser ultrasound (LU) technique has been used to determine dispersion curves for surface acoustic waves (SAW) propagating in AlScN/Al2O3 systems. Polar and non-polar Al0.77Sc0.23N thin films were prepared by magnetron sputter epitaxy on Al2 [...] Read more.
The laser ultrasound (LU) technique has been used to determine dispersion curves for surface acoustic waves (SAW) propagating in AlScN/Al2O3 systems. Polar and non-polar Al0.77Sc0.23N thin films were prepared by magnetron sputter epitaxy on Al2O3 substrates and coated with a metal layer. SAW dispersion curves have been measured for various propagation directions on the surface. This is easily achieved in LU measurements since no additional surface structures need to be fabricated, which would be required if elastic properties are determined with the help of SAW resonators. Variation of the propagation direction allows for efficient use of the system’s anisotropy when extracting information on elastic properties. This helps to overcome the complexity caused by a large number of elastic constants in the film material. An analysis of the sensitivity of the SAW phase velocities (with respect to the elastic moduli and their dependence on SAW propagation direction) reveals that the non-polar AlScN films are particularly well suited for the extraction of elastic film properties. Good agreement is found between experiment and theoretical predictions, validating LU as a non-destructive and fast technique for the determination of elastic constants of piezoelectric thin films. Full article
(This article belongs to the Special Issue Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices)
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9 pages, 1092 KiB  
Article
Characterization of Ferroelectric Al0.7Sc0.3N Thin Film on Pt and Mo Electrodes
by Ran Nie, Shuai Shao, Zhifang Luo, Xiaoxu Kang and Tao Wu
Micromachines 2022, 13(10), 1629; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13101629 - 28 Sep 2022
Cited by 9 | Viewed by 2356
Abstract
In the past decade, aluminum scandium nitride (AlScN) with a high Sc content has shown ferroelectric properties, which provides a new option for CMOS-process-compatible ferroelectric memory, sensors and actuators, as well as tunable devices. In this paper, the ferroelectric properties of [...] Read more.
In the past decade, aluminum scandium nitride (AlScN) with a high Sc content has shown ferroelectric properties, which provides a new option for CMOS-process-compatible ferroelectric memory, sensors and actuators, as well as tunable devices. In this paper, the ferroelectric properties of Al0.7Sc0.3N grown on different metals were studied. The effect of metal and abnormal orientation grains (AOGs) on ferroelectric properties was observed. A coercive field of approximately 3 MV/cm and a large remanent polarization of more than 100 μC/cm2 were exhibited on the Pt surface. The Al0.7Sc0.3N thin film grown on the Mo metal surface exhibited a large leakage current. We analyzed the leakage current of Al0.7Sc0.3N during polarization with the polarization frequency, and found that the Al0.7Sc0.3N films grown on either Pt or Mo surfaces have large leakage currents at frequencies below 5 kHz. The leakage current decreases significantly as the frequency approaches 10 kHz. The positive up negative down (PUND) measurement was used to obtain the remanent polarization of the films, and it was found that the remanent polarization values were not the same in the positive and negative directions, indicating that the electrode material has an effect on the ferroelectric properties. Full article
(This article belongs to the Special Issue Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices)
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10 pages, 4179 KiB  
Article
High Rate Deposition of Piezoelectric AlScN Films by Reactive Magnetron Sputtering from AlSc Alloy Targets on Large Area
by Stephan Barth, Tom Schreiber, Steffen Cornelius, Olaf Zywitzki, Thomas Modes and Hagen Bartzsch
Micromachines 2022, 13(10), 1561; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13101561 - 21 Sep 2022
Cited by 2 | Viewed by 1870
Abstract
This paper reports on the deposition and characterization of piezoelectric AlXSc1-XN (further: AlScN) films on Si substrates using AlSc alloy targets with 30 at.% Sc. Films were deposited on a Ø200 mm area with deposition rates of 200 nm/min [...] Read more.
This paper reports on the deposition and characterization of piezoelectric AlXSc1-XN (further: AlScN) films on Si substrates using AlSc alloy targets with 30 at.% Sc. Films were deposited on a Ø200 mm area with deposition rates of 200 nm/min using a reactive magnetron sputtering process with a unipolar–bipolar hybrid pulse mode of FEP. The homogeneity of film composition, structural properties and piezoelectric properties were investigated depending on process parameters, especially the pulse mode of powering in unipolar–bipolar hybrid pulse mode operation. Characterization methods include energy-dispersive spectrometry of X-ray (EDS), X-ray diffraction (XRD), piezoresponse force microscopy (PFM) and double-beam laser interferometry (DBLI). The film composition was Al0.695Sc0.295N. The films showed good homogeneity of film structure with full width at half maximum (FWHM) of AlScN(002) rocking curves at 2.2 ± 0.1° over the whole coating area when deposited with higher share of unipolar pulse mode during film growth. For a higher share of bipolar pulse mode, the films showed a much larger c-lattice parameter in the center of the coating area, indicating high in-plane compressive stress in the films. Rocking curve FWHM also showed similar values of 1.5° at the center to 3° at outer edge. The piezoelectric characterization method revealed homogenous d33,f of 11–12 pm/V for films deposited at a high share of unipolar pulse mode and distribution of 7–10 pm/V for a lower share of unipolar pulse mode. The films exhibited ferroelectric switching behavior with coercive fields of around 3–3.5 MV/cm and polarization of 80–120 µC/cm². Full article
(This article belongs to the Special Issue Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices)
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16 pages, 3258 KiB  
Article
Al1−xScxN Thin Films at High Temperatures: Sc-Dependent Instability and Anomalous Thermal Expansion
by Niklas Wolff, Md Redwanul Islam, Lutz Kirste, Simon Fichtner, Fabian Lofink, Agnė Žukauskaitė and Lorenz Kienle
Micromachines 2022, 13(8), 1282; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13081282 - 08 Aug 2022
Cited by 10 | Viewed by 2453
Abstract
Ferroelectric thin films of wurtzite-type aluminum scandium nitride (Al1−xScxN) are promising candidates for non-volatile memory applications and high-temperature sensors due to their outstanding functional and thermal stability exceeding most other ferroelectric thin film materials. In this work, the thermal [...] Read more.
Ferroelectric thin films of wurtzite-type aluminum scandium nitride (Al1−xScxN) are promising candidates for non-volatile memory applications and high-temperature sensors due to their outstanding functional and thermal stability exceeding most other ferroelectric thin film materials. In this work, the thermal expansion along with the temperature stability and its interrelated effects have been investigated for Al1−xScxN thin films on sapphire Al2O3(0001) with Sc concentrations x (x = 0, 0.09, 0.23, 0.32, 0.40) using in situ X-ray diffraction analyses up to 1100 °C. The selected Al1−xScxN thin films were grown with epitaxial and fiber textured microstructures of high crystal quality, dependent on the choice of growth template, e.g., epitaxial on Al2O3(0001) and fiber texture on Mo(110)/AlN(0001)/Si(100). The presented studies expose an anomalous regime of thermal expansion at high temperatures >~600 °C, which is described as an isotropic expansion of a and c lattice parameters during annealing. The collected high-temperature data suggest differentiation of the observed thermal expansion behavior into defect-coupled intrinsic and oxygen-impurity-coupled extrinsic contributions. In our hypothesis, intrinsic effects are denoted to the thermal activation, migration and curing of defect structures in the material, whereas extrinsic effects describe the interaction of available oxygen species with these activated defect structures. Their interaction is the dominant process at high temperatures >800 °C resulting in the stabilization of larger modifications of the unit cell parameters than under exclusion of oxygen. The described phenomena are relevant for manufacturing and operation of new Al1−xScxN-based devices, e.g., in the fields of high-temperature resistant memory or power electronic applications. Full article
(This article belongs to the Special Issue Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices)
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13 pages, 4767 KiB  
Article
Compensation of the Stress Gradient in Physical Vapor Deposited Al1−xScxN Films for Microelectromechanical Systems with Low Out-of-Plane Bending
by Rossiny Beaucejour, Michael D’Agati, Kritank Kalyan and Roy H. Olsson III
Micromachines 2022, 13(8), 1169; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13081169 - 24 Jul 2022
Cited by 6 | Viewed by 2057
Abstract
Thin film through-thickness stress gradients produce out-of-plane bending in released microelectromechanical systems (MEMS) structures. We study the stress and stress gradient of Al0.68Sc0.32N thin films deposited directly on Si. We show that Al0.68Sc0.32N cantilever structures [...] Read more.
Thin film through-thickness stress gradients produce out-of-plane bending in released microelectromechanical systems (MEMS) structures. We study the stress and stress gradient of Al0.68Sc0.32N thin films deposited directly on Si. We show that Al0.68Sc0.32N cantilever structures realized in films with low average film stress have significant out-of-plane bending when the Al1−xScxN material is deposited under constant sputtering conditions. We demonstrate a method where the total process gas flow is varied during the deposition to compensate for the native through-thickness stress gradient in sputtered Al1−xScxN thin films. This method is utilized to reduce the out-of-plane bending of 200 µm long, 500 nm thick Al0.68Sc0.32N MEMS cantilevers from greater than 128 µm to less than 3 µm. Full article
(This article belongs to the Special Issue Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices)
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19 pages, 6135 KiB  
Article
Vertical and Lateral Etch Survey of Ferroelectric AlN/Al1−xScxN in Aqueous KOH Solutions
by Zichen Tang, Giovanni Esteves, Jeffrey Zheng and Roy H. Olsson III
Micromachines 2022, 13(7), 1066; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13071066 - 02 Jul 2022
Cited by 8 | Viewed by 3499
Abstract
Due to their favorable electromechanical properties, such as high sound velocity, low dielectric permittivity and high electromechanical coupling, Aluminum Nitride (AlN) and Aluminum Scandium Nitride (Al1−xScxN) thin films have achieved widespread application in radio frequency (RF) acoustic devices. The [...] Read more.
Due to their favorable electromechanical properties, such as high sound velocity, low dielectric permittivity and high electromechanical coupling, Aluminum Nitride (AlN) and Aluminum Scandium Nitride (Al1−xScxN) thin films have achieved widespread application in radio frequency (RF) acoustic devices. The resistance to etching at high scandium alloying, however, has inhibited the realization of devices able to exploit the highest electromechanical coupling coefficients. In this work, we investigated the vertical and lateral etch rates of sputtered AlN and Al1−xScxN with Sc concentration x ranging from 0 to 0.42 in aqueous potassium hydroxide (KOH). Etch rates and the sidewall angles were reported at different temperatures and KOH concentrations. We found that the trends of the etch rate were unanimous: while the vertical etch rate decreases with increasing Sc alloying, the lateral etch rate exhibits a V-shaped transition with a minimum etch rate at x = 0.125. By performing an etch on an 800 nm thick Al0.875Sc0.125N film with 10 wt% KOH at 65 °C for 20 min, a vertical sidewall was formed by exploiting the ratio of the 1011¯ planes and 11¯00 planes etch rates. This method does not require preliminary processing and is potentially beneficial for the fabrication of lamb wave resonators (LWRs) or other microelectromechanical systems (MEMS) structures, laser mirrors and Ultraviolet Light-Emitting Diodes (UV-LEDs). It was demonstrated that the sidewall angle tracks the trajectory that follows the 1¯212¯ of the hexagonal crystal structure when different c/a ratios were considered for elevated Sc alloying levels, which may be used as a convenient tool for structure/composition analysis. Full article
(This article belongs to the Special Issue Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices)
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9 pages, 1311 KiB  
Article
SAW Resonators and Filters Based on Sc0.43Al0.57N on Single Crystal and Polycrystalline Diamond
by Miguel Sinusia Lozano, Laura Fernández-García, David López-Romero, Oliver A. Williams and Gonzalo F. Iriarte
Micromachines 2022, 13(7), 1061; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13071061 - 30 Jun 2022
Cited by 5 | Viewed by 2139
Abstract
The massive data transfer rates of nowadays mobile communication technologies demand devices not only with outstanding electric performances but with example stability in a wide range of conditions. Surface acoustic wave (SAW) devices provide a high Q-factor and properties inherent to the employed [...] Read more.
The massive data transfer rates of nowadays mobile communication technologies demand devices not only with outstanding electric performances but with example stability in a wide range of conditions. Surface acoustic wave (SAW) devices provide a high Q-factor and properties inherent to the employed materials: thermal and chemical stability or low propagation losses. SAW resonators and filters based on Sc0.43Al0.57N synthetized by reactive magnetron sputtering on single crystal and polycrystalline diamond substrates were fabricated and evaluated. Our SAW resonators showed high electromechanical coupling coefficients for Rayleigh and Sezawa modes, propagating at 1.2 GHz and 2.3 GHz, respectively. Finally, SAW filters were fabricated on Sc0.43Al0.57N/diamond heterostructures, with working frequencies above 4.7 GHz and ~200 MHz bandwidths, confirming that these devices are promising candidates in developing 5G technology. Full article
(This article belongs to the Special Issue Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices)
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11 pages, 4161 KiB  
Article
Dual-Mode Scandium-Aluminum Nitride Lamb-Wave Resonators Using Reconfigurable Periodic Poling
by Sushant Rassay, Dicheng Mo and Roozbeh Tabrizian
Micromachines 2022, 13(7), 1003; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13071003 - 26 Jun 2022
Cited by 9 | Viewed by 2155
Abstract
This paper presents the use of ferroelectric behavior in scandium–aluminum nitride (ScxAl1−xN) to create dual-mode Lamb-wave resonators for the realization of intrinsically configurable radio-frequency front-end systems. An integrated array of intrinsically switchable dual-mode Lamb-wave resonators with frequencies covering the [...] Read more.
This paper presents the use of ferroelectric behavior in scandium–aluminum nitride (ScxAl1−xN) to create dual-mode Lamb-wave resonators for the realization of intrinsically configurable radio-frequency front-end systems. An integrated array of intrinsically switchable dual-mode Lamb-wave resonators with frequencies covering the 0.45–3 GHz spectrum. The resonators are created in ferroelectric scandium–aluminum nitride (Sc0.28Al0.72N) film and rely on period poling for intrinsic configuration between Lamb modes with highly different wavelengths and frequencies. A comprehensive analytical model is presented, formulating intrinsically switchable dual-mode operation and providing closed-form derivation of electromechanical coupling (kt2) in the two resonance modes as a function of electrode dimensions and scandium content. Fabricated resonator prototypes show kt2s as high as 4.95%, when operating in the first modes over 0.45–1.6 GHz, 2.23% when operating in the second mode of operation over 0.8–3 GHz, and series quality factors (Qs) over 300–800. Benefiting from lithographical frequency tailorability and intrinsic switchability that alleviate the need for external multiplexers, and large kt2 and Q, dual-mode Sc0.28Al0.72N Lamb-wave resonators are promising candidates to realize single-chip multi-band reconfigurable spectral processors for radio-frequency front-ends of modern wireless systems. Full article
(This article belongs to the Special Issue Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices)
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9 pages, 2612 KiB  
Article
High-Temperature Ferroelectric Behavior of Al0.7Sc0.3N
by Daniel Drury, Keisuke Yazawa, Andriy Zakutayev, Brendan Hanrahan and Geoff Brennecka
Micromachines 2022, 13(6), 887; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13060887 - 31 May 2022
Cited by 25 | Viewed by 3282
Abstract
Currently, there is a lack of nonvolatile memory (NVM) technology that can operate continuously at temperatures > 200 °C. While ferroelectric NVM has previously demonstrated long polarization retention and >1013 read/write cycles at room temperature, the largest hurdle comes at higher temperatures [...] Read more.
Currently, there is a lack of nonvolatile memory (NVM) technology that can operate continuously at temperatures > 200 °C. While ferroelectric NVM has previously demonstrated long polarization retention and >1013 read/write cycles at room temperature, the largest hurdle comes at higher temperatures for conventional perovskite ferroelectrics. Here, we demonstrate how AlScN can enable high-temperature (>200 °C) nonvolatile memory. The c-axis textured thin films were prepared via reactive radiofrequency magnetron sputtering onto a highly textured Pt (111) surface. Photolithographically defined Pt top electrodes completed the capacitor stack, which was tested in a high temperature vacuum probe station up to 400 °C. Polarization–electric field hysteresis loops between 23 and 400 °C reveal minimal changes in the remanent polarization values, while the coercive field decreased from 4.3 MV/cm to 2.6 MV/cm. Even at 400 °C, the polarization retention exhibited negligible loss for up to 1000 s, demonstrating promise for potential nonvolatile memory capable of high−temperature operation. Fatigue behavior also showed a moderate dependence on operating temperature, but the mechanisms of degradation require additional study. Full article
(This article belongs to the Special Issue Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices)
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11 pages, 5021 KiB  
Article
Effect of Substrate-RF on Sub-200 nm Al0.7Sc0.3N Thin Films
by Michele Pirro, Xuanyi Zhao, Bernard Herrera, Pietro Simeoni and Matteo Rinaldi
Micromachines 2022, 13(6), 877; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13060877 - 31 May 2022
Cited by 9 | Viewed by 2063
Abstract
Sc-doped aluminum nitride is emerging as a new piezoelectric material which can substitute undoped aluminum nitride (AlN) in radio-frequency MEMS applications, thanks to its demonstrated enhancement of the piezoelectric coefficients. Furthermore, the recent demonstration of the ferroelectric-switching capability of the material gives AlScN [...] Read more.
Sc-doped aluminum nitride is emerging as a new piezoelectric material which can substitute undoped aluminum nitride (AlN) in radio-frequency MEMS applications, thanks to its demonstrated enhancement of the piezoelectric coefficients. Furthermore, the recent demonstration of the ferroelectric-switching capability of the material gives AlScN the possibility to integrate memory functionalities in RF components. However, its high-coercive field and high-leakage currents are limiting its applicability. Residual stress, growth on different substrates, and testing-temperature have already been demonstrated as possible knobs to flatten the energy barrier needed for switching, but no investigation has been reported yet on the whole impact on the dielectric and ferroelectric dynamic behavior of a single process parameter. In this context, we analyze the complete spectrum of variations induced by the applied substrate-RF, from deposition characteristics to dielectric and ferroelectric properties, proving its effect on all of the material attributes. In particular, we demonstrate the possibility of engineering the AlScN lattice cell to properly modify leakage, breakdown, and coercive fields, as well as polarization charge, without altering the crystallinity level, making substrate-RF an effective and efficient fabrication knob to ease the limitations the material is facing. Full article
(This article belongs to the Special Issue Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices)
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9 pages, 2858 KiB  
Article
Growth of Highly c-Axis Oriented AlScN Films on Commercial Substrates
by Jingxiang Su, Simon Fichtner, Muhammad Zubair Ghori, Niklas Wolff, Md. Redwanul Islam, Andriy Lotnyk, Dirk Kaden, Florian Niekiel, Lorenz Kienle, Bernhard Wagner and Fabian Lofink
Micromachines 2022, 13(5), 783; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13050783 - 17 May 2022
Cited by 11 | Viewed by 3620
Abstract
In this work, we present a method for growing highly c-axis oriented aluminum scandium nitride (AlScN) thin films on (100) silicon (Si), silicon dioxide (SiO2) and epitaxial polysilicon (poly-Si) substrates using a substrate independent approach. The presented method offers great [...] Read more.
In this work, we present a method for growing highly c-axis oriented aluminum scandium nitride (AlScN) thin films on (100) silicon (Si), silicon dioxide (SiO2) and epitaxial polysilicon (poly-Si) substrates using a substrate independent approach. The presented method offers great advantages in applications such as piezoelectric thin-film-based surface acoustic wave devices where a metallic seed layer cannot be used. The approach relies on a thin AlN layer to establish a wurtzite nucleation layer for the growth of w-AlScN films. Both AlScN thin film and seed layer AlN are prepared by DC reactive magnetron sputtering process where a Sc concentration of 27% is used throughout this study. The crystal quality of (0002) orientation of Al0.73Sc0.27N films on all three substrates is significantly improved by introducing a 20 nm AlN seed layer. Although AlN has a smaller capacitance than AlScN, limiting the charge stored on the electrode plates, the combined piezoelectric coefficient d33,f with 500 nm AlScN is only slightly reduced by about 4.5% in the presence of the seed layer. Full article
(This article belongs to the Special Issue Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices)
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13 pages, 16821 KiB  
Article
Static High Voltage Actuation of Piezoelectric AlN and AlScN Based Scanning Micromirrors
by Chris Stoeckel, Katja Meinel, Marcel Melzer, Agnė Žukauskaitė, Sven Zimmermann, Roman Forke, Karla Hiller and Harald Kuhn
Micromachines 2022, 13(4), 625; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13040625 - 15 Apr 2022
Cited by 3 | Viewed by 2259
Abstract
Piezoelectric micromirrors with aluminum nitride (AlN) and aluminum scandium nitride (Al0.68Sc0.32N) are presented and compared regarding their static deflection. Two chip designs with 2 × 3 mm2 (Design 1) and 4 × 6 mm2 (Design 2) footprint [...] Read more.
Piezoelectric micromirrors with aluminum nitride (AlN) and aluminum scandium nitride (Al0.68Sc0.32N) are presented and compared regarding their static deflection. Two chip designs with 2 × 3 mm2 (Design 1) and 4 × 6 mm2 (Design 2) footprint with 600 nm AlN or 2000 nm Al0.68Sc0.32N as piezoelectric transducer material are investigated. The chip with Design 1 and Al0.68Sc0.32N has a resonance frequency of 1.8 kHz and a static scan angle of 38.4° at 400 V DC was measured. Design 2 has its resonance at 2.1 kHz. The maximum static scan angle is 55.6° at 220 V DC, which is the maximum deflection measurable with the experimental setup. The static deflection per electric field is increased by a factor of 10, due to the optimization of the design and the research and development of high-performance piezoelectric transducer materials with large piezoelectric coefficient and high electrical breakthrough voltage. Full article
(This article belongs to the Special Issue Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices)
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