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Preparation, Characterization and Application of Metal Oxide Thin Films

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Thin Films and Interfaces".

Deadline for manuscript submissions: closed (20 May 2023) | Viewed by 29101

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Special Issue Editor

Prof. Dr. Hee Chul Lee

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Guest Editor

Functional Electronic Materials LAB, Department of Advanced Materials Engineering, Korea Polytechnic University, 237 Sangidaehak-ro, Siheung-si 15073, Gyeonggi-do, Korea
Interests: ferroelectric memories; thin film deposition; plasma processing; solid electrolyte; all-solid lithium ion batteries; piezoelectric devices

Special Issue Information

Dear Colleagues,

Metal oxide thin films have been widely used in various applications such as sensors, semiconductors, displays, and optical fields. There are various techniques, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition(ALD), and sol–gel coating as methods for forming metal oxide thin films. Such metal oxide films could have a porous or very dense structure. Our aim is for this Special Issue to broadly cover the formation mechanism of structure of metal oxide thin films, unique methods for analyzing these thin films, and their potential applications to high-tech industry. Additionally, even if not included in the list below, this Special Issue invites papers from the very wide research fields adjacent to or indirectly related to metal oxide thin films.

Prof. Hee Chul Lee
Guest Editor

Manuscript Submission Information

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Keywords

Metal oxide thin films
Physical vapor deposition (PVD)
Chemical vapor deposition (CVD)
Atomic layer deposition (ALD)
Plasma-enhanced deposition
Sol–gel coating
Thin film analysis
Sensor devices
Thin film transistors
Optoelectronic application

Published Papers (14 papers)

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Research

11 pages, 4147 KiB

Open AccessArticle

Synthesis of Planar-Type ZnO Powder in Non-Nano Scale Dimension and Its Application in Ultraviolet Protection Cosmetics

by Jung-Hwan Lee, Gun-Sub Lee, Eung-Nam Park, Dong-Hyeon Jo, So-Won Kim and Hee-Chul Lee

Materials 2023, 16(5), 2099; https://doi.org/10.3390/ma16052099 - 05 Mar 2023

Cited by 3 | Viewed by 1667

Abstract

ZnO is one of the most widely used inorganic sunscreens, owing to its fine particle size and UV light shielding capability. However, powders at nanosizes can be toxic and cause adverse effects. The development of non-nanosized particles has been slow. The present work investigated synthesis methods of non-nanosized ZnO particles for ultraviolet protection application. By altering the starting material, KOH concentration, and input speed, the ZnO particles can be obtained in different forms, including needle type, planar type, and vertical wall type. Cosmetic samples were made by mixing different ratios of synthesized powders. The physical properties and the UV blockage efficacy of different samples were evaluated using scanning electron microscopy (SEM), X-ray diffraction (XRD), particle size analyzer (PSA), and ultraviolet/visible (UV/Vis) spectrometer. The samples with 1:1 ratio of needle-type ZnO and vertical wall-type ZnO exhibited superior light blocking effect owing to improved dispersibility and prevention of particle agglomeration. The 1:1 mixed sample also complied with the European nanomaterials regulation due to the absence of nanosized particles. With superior UV protection in the UVA and UVB regions, the 1:1 mixed powder showed potential to be used as a main ingredient in UV protection cosmetics. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)

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13 pages, 3897 KiB

Open AccessEditor’s ChoiceArticle

Effect of a ZrO₂ Seed Layer on an Hf_0.5Zr_0.5O₂ Ferroelectric Device Fabricated via Plasma Enhanced Atomic Layer Deposition

by Ji-Na Song, Min-Jung Oh and Chang-Bun Yoon

Materials 2023, 16(5), 1959; https://doi.org/10.3390/ma16051959 - 27 Feb 2023

Cited by 1 | Viewed by 1848

Abstract

In this study, a ferroelectric layer was formed on a ferroelectric device via plasma enhanced atomic layer deposition. The device used 50 nm thick TiN as upper and lower electrodes, and an Hf_0.5Zr_0.5O₂ (HZO) ferroelectric material was applied to fabricate a metal–ferroelectric–metal-type capacitor. HZO ferroelectric devices were fabricated in accordance with three principles to improve their ferroelectric properties. First, the HZO nanolaminate thickness of the ferroelectric layers was varied. Second, heat treatment was performed at 450, 550, and 650 °C to investigate the changes in the ferroelectric characteristics as a function of the heat-treatment temperature. Finally, ferroelectric thin films were formed with or without seed layers. Electrical characteristics such as the I–E characteristics, P–E hysteresis, and fatigue endurance were analyzed using a semiconductor parameter analyzer. The crystallinity, component ratio, and thickness of the nanolaminates of the ferroelectric thin film were analyzed via X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The residual polarization of the (20,20)*3 device heat treated at 550 °C was 23.94 μC/cm², whereas that of the D(20,20)*3 device was 28.18 μC/cm², which improved the characteristics. In addition, in the fatigue endurance test, the wake-up effect was observed in specimens with bottom and dual seed layers, which exhibited excellent durability after 10⁸ cycles. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)

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11 pages, 3422 KiB

Open AccessArticle

Facile Synthesis of Two Dimensional (2D) V₂O₅ Nanosheets Film towards Photodetectors

by Shaotian Wang, Liangfei Wu, Hui Zhang, Zihan Wang, Qinggang Qin, Xi Wang, Yuan Lu, Liang Li and Ming Li

Materials 2022, 15(23), 8313; https://doi.org/10.3390/ma15238313 - 23 Nov 2022

Cited by 7 | Viewed by 1639

Abstract

Most of the studies focused on V₂O₅ have been devoted to obtaining specific morphology and microstructure for its intended applications. Two dimensional (2D) V₂O₅ has the most valuable structure because of its unique planar configuration that can offer more active sites. In this study, a bottom-up and low-cost method that is hydrothermal combined with spin-coating and subsequent annealing was developed to prepare 2D V₂O₅ nanosheets film on quartz substrate. First, VOOH nanosheets were prepared by the hydrothermal method using V₂O₅ powders and EG as raw materials. Further, V₂O₅ nanosheets with an average lateral size over 500 nm and thickness less than 10 nm can be prepared from the parent VOOH nanosheets by annealing at 350 °C for 15 min in air. The prepared V₂O₅ nanosheets film was assembled of multiple nanosheets. The structural, morphological, microstructural and optical properties of the films were respective investigated by XRD, SEM, TEM and UV-Vis. The photodetector based on V₂O₅ nanosheets film shows good photoresponse with a response time of 2.4 s and a recovery time of 4.7 s. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)

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10 pages, 2602 KiB

Open AccessEditor’s ChoiceArticle

Characterization of Porous CuO Films for H₂S Gas Sensors

by Dawoon Jung, Sehoon Hwang, Hyun-Jong Kim, Jae-Hee Han and Ho-Nyun Lee

Materials 2022, 15(20), 7270; https://doi.org/10.3390/ma15207270 - 18 Oct 2022

Cited by 5 | Viewed by 1446

Abstract

Using a thermal evaporator, various porous Cu films were deposited according to the deposition pressure. CuO films were formed by post heat treatment in the air. Changes in morphological and structural characteristics of films were analyzed using field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). Relative density and porosity were quantitatively calculated. CuO films with various pores ranging from 39.4 to 95.2% were successfully manufactured and were applied as gas sensors for H₂S detection on interdigitated electrode (IDE) substrate. Resistance change was monitored at 325 °C and an increase in porosity of the film improved the sensor performance. The CuO-10 gas sensor with a high porosity of 95.2% showed a relatively high response (2.7) and a fast recovery time (514 s) for H₂S 1.5 ppm. It is confirmed that the porosity of the CuO detection layer had a significant effect on response and recovery time. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)

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12 pages, 4367 KiB

Open AccessArticle

Development of PZN-PMN-PZT Piezoelectric Ceramics with High d₃₃ and Q_m Values

by So-Won Kim and Hee-Chul Lee

Materials 2022, 15(20), 7070; https://doi.org/10.3390/ma15207070 - 11 Oct 2022

Cited by 6 | Viewed by 2325

Abstract

To achieve good long-term temperature stability in devices used in energy-conversion applications, this study is aimed at developing combined ceramics, referred to as PZN-PMN-PZT, comprising Pb(Zn_1/3Nb_2/3)O₃ (PZN) and Pb(Mn_1/3Nb_2/3)O₃ (PMN), which are typical relaxor ferroelectric materials, and Pb(Zr_,Ti)O₃ (PZT). The piezoelectric properties were compared based on several parameters according to the change in the composition ratio between relaxor materials, amounts of Sb₂O₃ dopant, and Zr/Ti ratio in the PZT system. Finally, we established optimal poling conditions to improve the electrical properties of the optimized piezoelectric material, based on the evaluation of ceramic properties according to the applied voltage during the poling process. The optimized composition of the investigated piezoelectric ceramics is represented by 0.14PZN-0.06PMN-0.80PbZr_0.49Ti_0.51 + 0.3 wt.% CuO + 0.3 wt.% Fe₂O₃ with 0.1 wt.% Sb₂O₃ doping, which yielded the superior properties (d₃₃ = 361 pC/N, Q_m = 1234, T_c = 306 °C). Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)

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22 pages, 4755 KiB

Open AccessArticle

Tuning the Porosity of Piezoelectric Zinc Oxide Thin Films Obtained from Molecular Layer-Deposited “Zincones”

by Marianne Kräuter, Taher Abu Ali, Barbara Stadlober, Roland Resel, Katrin Unger and Anna Maria Coclite

Materials 2022, 15(19), 6786; https://doi.org/10.3390/ma15196786 - 30 Sep 2022

Cited by 1 | Viewed by 1489

Abstract

Porous zinc oxide (ZnO) thin films were synthesized via the calcination of molecular layer-deposited (MLD) “zincone” layers. The effect of the MLD process temperature (110 °C, 125 °C) and of the calcination temperature (340 °C, 400 °C, 500 °C) on the chemical, morphological, and crystallographic properties of the resulting ZnO was thoroughly investigated. Spectroscopic ellipsometry reveals that the thickness of the calcinated layers depends on the MLD temperature, resulting in 38–43% and 52–56% of remaining thickness for the 110 °C and 125 °C samples, respectively. Ellipsometric porosimetry shows that the open porosity of the ZnO thin films depends on the calcination temperature as well as on the MLD process temperature. The maximum open porosity of ZnO derived from zincone deposited at 110 °C ranges from 14.5% to 24%, rising with increasing calcination temperature. Compared with the 110 °C samples, the ZnO obtained from 125 °C zincone yields a higher porosity for low calcination temperatures, namely 18% for calcination at 340 °C; and up to 24% for calcination at 500 °C. Additionally, the porous ZnO thin films were subjected to piezoelectric measurements. The piezoelectric coefficient, d₃₃, was determined to be 2.8 pC/N, demonstrating the potential of the porous ZnO as an, e.g., piezoelectric sensor or energy harvester. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)

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15 pages, 5475 KiB

Open AccessArticle

Effect of Pre-Anodized Film on Micro-Arc Oxidation Process of 6063 Aluminum Alloy

by Linwei Li, Erhui Yang, Zhibin Yan, Xiaomeng Xie, Wu Wei and Weizhou Li

Materials 2022, 15(15), 5221; https://doi.org/10.3390/ma15155221 - 28 Jul 2022

Cited by 6 | Viewed by 1403

Abstract

In the current investigation, micro-arc oxidation (MAO) ceramic coatings on aluminum are galvanostatically synthesized at various processing stages in an alkaline silicate system. The resultant coatings are systematically investigated in terms of the following respects: The working voltage and surface sparking evolution over the studied course of MAO are recorded by the signal acquisition system and the real-time imaging, respectively; the phase composition, the surface morphology, and the polished cross-section of the coatings are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) assisted with an energy-dispersive X-ray spectrometer (EDS), respectively. In particular, with the help of a low-rate increase in working voltage, the evolution of the sparks, the energy consumption, and the microstructure development of aluminum in alkaline silicate electrolyte by pre-anodizing are systematically investigated. The results show that the pre-anodized film can accelerate the evolution process of MAO spark and shorten the reaction process in the early stage of MAO reaction, reducing energy consumption and improving the corrosion resistance of the MAO coating. The γ-Al2O3 phase content after pre-anodized is significantly increased in MAO coatings. In particular, the thicker the pre-anodized film (beyond 8 μm) was broken down and fragmentation thinning in the early stage of the MAO process with the presence of micro discharges. This is due to the fact that the electron transition will be released by the emission of radiative recombination and reveals obvious galvanoluminescence (GL) behavior on the surface of the pre-anodized film. Further, based on the present MAO coating microstructure, a model of coating growth after pre-anodized that evolves over time is proposed. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)

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15 pages, 6805 KiB

Open AccessArticle

Surface Morphology of Textured Transparent Conductive Oxide Thin Film Seen by Various Probes: Visible Light, X-rays, Electron Scattering and Contact Probe

by Krunoslav Juraić, Pavo Dubček, Mario Bohač, Andreja Gajović, Sigrid Bernstorff, Miran Čeh, Aden Hodzic and Davor Gracin

Materials 2022, 15(14), 4814; https://doi.org/10.3390/ma15144814 - 10 Jul 2022

Cited by 3 | Viewed by 1837

Abstract

Fluorine-doped tin oxide thin films (SnO₂:F) are widely used as transparent conductive oxide electrodes in thin-film solar cells because of their appropriate electrical and optical properties. The surface morphology of these films influences their optical properties and therefore plays an important role in the overall efficiencies of the solar cells in which they are implemented. At rough surfaces light is diffusely scattered, extending the optical path of light inside the active layer of the solar cell, which in term improves light absorption and solar cell conversion efficiency. In this work, we investigated the surface morphology of undoped and doped SnO₂ thin films and their influence on the optical properties of the films. We have compared and analysed the results obtained by several complementary methods for thin-film surface morphology investigation: atomic force microscopy (AFM), transmission electron microscopy (TEM), and grazing-incidence small-angle X-ray scattering (GISAXS). Based on the AFM and TEM results we propose a theoretical model that reproduces well the GISAXS scattering patterns. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)

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10 pages, 2452 KiB

Open AccessEditor’s ChoiceArticle

Si-Doped HfO₂-Based Ferroelectric Tunnel Junctions with a Composite Energy Barrier for Non-Volatile Memory Applications

by Yoseop Lee, Sungmun Song, Woori Ham and Seung-Eon Ahn

Materials 2022, 15(6), 2251; https://doi.org/10.3390/ma15062251 - 18 Mar 2022

Cited by 15 | Viewed by 2851

Abstract

Ferroelectric tunnel junctions (FTJs) have attracted attention as devices for advanced memory applications owing to their high operating speed, low operating energy, and excellent scalability. In particular, hafnia ferroelectric materials are very promising because of their high remanent polarization (below 10 nm) and high compatibility with complementary metal-oxide-semiconductor (CMOS) processes. In this study, a Si-doped HfO₂-based FTJ device with a metal-ferroelectric-insulator-semiconductor (MFIS) structure was proposed to maximize the tunneling electro-resistance (TER) effect. The potential barrier modulation effect under applied varying voltage was analyzed, and the possibility of its application as a non-volatile memory device was presented through stability assessments such as endurance and retention tests. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)

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12 pages, 26822 KiB

Open AccessArticle

Flexible Ni/NiO_x-Based Sensor for Human Breath Detection

by Le Duc-Anh Ho, Vu Binh Nam and Daeho Lee

Materials 2022, 15(1), 47; https://doi.org/10.3390/ma15010047 - 22 Dec 2021

Cited by 9 | Viewed by 3179

Abstract

We developed a simple methodology to fabricate an Ni/NiO_x-based flexible breath sensor by a single-step laser digital patterning process of solution-processed NiO_x thin-film deposited using NiO_x nanoparticle ink. Laser-induced reductive sintering phenomenon enables for the generation of three parts of Ni electrodes and two narrow NiO_x-sensing channels in between, defined on a single layer on a thin flexible polymer substrate. The Ni/NiO_x-based breath sensor efficiently detects human breath at a relatively low operating temperature (50 °C) with fast response/recovery times (1.4 s/1.7 s) and excellent repeatability. The mechanism of the gas-sensing ability enhancement of the sensor was investigated by X-ray photoelectron spectroscopy analysis. Furthermore, by decoupling of the temperature effect from the breathing gas, the response of the sensor due to the temperature alone and due to the chemical components in the breathing gas could be separately evaluated. Finally, bending and cyclic bending tests (10,000 cycles) demonstrated the superior mechanical stability of the flexible breath sensor. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)

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8 pages, 1174 KiB

Open AccessArticle

Synaptic Transistors Exhibiting Gate-Pulse-Driven, Metal-Semiconductor Transition of Conduction

by Jung Wook Lim, Su Jae Heo, Min A. Park and Jieun Kim

Materials 2021, 14(24), 7508; https://doi.org/10.3390/ma14247508 - 07 Dec 2021

Cited by 2 | Viewed by 2074

Abstract

Neuromorphic devices have been investigated extensively for technological breakthroughs that could eventually replace conventional semiconductor devices. In contrast to other neuromorphic devices, the device proposed in this paper utilizes deep trap interfaces between the channel layer and the charge-inducing dielectrics (CID). The device was fabricated using in-situ atomic layer deposition (ALD) for the sequential deposition of the CID and oxide semiconductors. Upon the application of a gate bias pulse, an abrupt change in conducting states was observed in the device from the semiconductor to the metal. Additionally, numerous intermediate states could be implemented based on the number of cycles. Furthermore, each state persisted for 10,000 s after the gate pulses were removed, demonstrating excellent synaptic properties of the long-term memory. Moreover, the variation of drain current with cycle number demonstrates the device’s excellent linearity and symmetry for excitatory and inhibitory behaviors when prepared on a glass substrate intended for transparent devices. The results, therefore, suggest that such unique synaptic devices with extremely stable and superior properties could replace conventional semiconducting devices in the future. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)

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11 pages, 5209 KiB

Open AccessArticle

New Simulation Method for Dependency of Device Degradation on Bending Direction and Channel Length

by Yunyeong Choi, Jisun Park and Hyungsoon Shin

Materials 2021, 14(20), 6167; https://doi.org/10.3390/ma14206167 - 18 Oct 2021

Cited by 2 | Viewed by 1469

Abstract

The dependency of device degradation on bending direction and channel length is analyzed in terms of bandgap states in amorphous indium-gallium-zinc-oxide (a-IGZO) films. The strain distribution in an a-IGZO film under perpendicular and parallel bending of a device with various channel lengths is investigated by conducting a three-dimensional mechanical simulation. Based on the obtained strain distribution, new device simulation structures are suggested in which the active layer is defined as consisting of multiple regions. The different arrangements of a highly strained region and density of states is proportional to the strain account for the measurement tendency. The analysis performed using the proposed structures reveals the causes underlying the effects of different bending directions and channel lengths, which cannot be explained using the existing simulation methods in which the active layer is defined as a single region. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)

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11 pages, 4243 KiB

Open AccessArticle

Fabrication of Highly Porous and Pure Zinc Oxide Films Using Modified DC Magnetron Sputtering and Post-Oxidation

by Se-Yong Park, Soon-Ho Rho, Hwan-Seok Lee, Kyoung-Min Kim and Hee-Chul Lee

Materials 2021, 14(20), 6112; https://doi.org/10.3390/ma14206112 - 15 Oct 2021

Cited by 6 | Viewed by 1543

Abstract

Porous films of metals and metal oxides exhibit larger surface areas and higher reactivities than those of dense films. Therefore, they have gained growing attention as potential materials for use in various applications. This study reports the use of a modified direct current magnetron sputtering method to form porous Zn-ZnO composite films, wherein a subsequent wet post-oxidation process is employed to fabricate pure porous ZnO films. The porous Zn-ZnO composite films were initially formed in clusters, and evaluation of their resulting properties allowed the optimal conditions to be determined. An oxygen ratio of 0.3% in the argon gas flow resulted in the best porosity, while a process pressure of 14 mTorr was optimal. Following deposition, porous ZnO films were obtained through rapid thermal annealing in the presence of water vapor, and the properties and porosities of the obtained films were analyzed. An oxidation temperature of 500 °C was optimal, with an oxidation time of 5 min giving a pure ZnO film with 26% porosity. Due to the fact that the films produced using this method are highly reliable, they could be employed in applications that require large specific surface areas, such as sensors, supercapacitors, and batteries. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Metal Oxide Thin Films)

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14 pages, 3616 KiB

Open AccessArticle

Piezoelectric Ceramics with High d₃₃ Constants and Their Application to Film Speakers

by Sowon Kim and Heechul Lee

Materials 2021, 14(19), 5795; https://doi.org/10.3390/ma14195795 - 03 Oct 2021

Cited by 4 | Viewed by 3007

Abstract

A multilayer piezoelectric material was fabricated using piezoelectric materials with low-temperature sintering capabilities and high piezoelectric coefficients to develop a functionally superior piezoelectric speaker with a large-displacement deformation. A soft relaxor was utilized to prepare the component materials, with the optimized composition of [...] Read more.

0.2 P b ({(Z n_{0.8} N i_{0.2})}_{\frac{1}{3}} N b_{\frac{2}{3}}) O_{3} - 0.8 P b (Z r_{0.5} T i_{0.5}) O_{3}

L i_{2} C O_{3}

was added to assist the low-temperature sintering conducted at 875 °C, which yielded a multilayer piezoelectric material with superior properties (

d_{33}

= 500 pC N⁻¹,

k_{p}

= 0.63,

g_{33}

= 44 mV N⁻¹). A multilayer piezoelectric actuator with a single-layer thickness of ~40 µm and dimensions of 12 × 16 mm² was fabricated by tape casting the prepared green sheets. Finite element analysis revealed that the use of a PEEK film and a smaller silicone–rubber film as a composite in the diaphragm realized optimal frequency-response characteristics; the vibrations generated by the piezoelectric element were amplified. The optimal structure obtained via simulations was applied to fabricate an actual piezoelectric speaker with dimensions of 20 × 24 × 1 mm³. The actual measurements exhibited a sound pressure level of ~75 dB and a total harmonic distortion ≤15% in the audible frequency range (250–20,000 Hz) at an applied voltage of 5