Atomic Layer Deposition Process Research Articles

Two-step ALD process for non-oxide ceramic deposition: the example of boron nitride

Atomic layer deposition (ALD) based on polymer-derived ceramics (PDCs) chemistry is used for the fabrication of boron nitride thin films from reaction between trichloroborazine and hexamethyldisilazane. The transposition of the PDCs route to ALD is highly appealing for depositing ceramics, especially non-oxide ones, as it offers various molecular precursors. From a two-step approach composed of an ALD process forming a so-called preceramic film and its subsequent ceramization, conformal and homogenous BN layers are successfully synthesized on various inorganic substrates. In the first stage, smooth polyborazine coatings are obtained at a temperature as low as 90 °C. The saturation and self-limitation of the ALD gas-surface reactions are verified. Intriguingly, three ALD windows seem to exist and are attributed to change in ligand exchange. After the ceramization stage using a heat treatment, conformal near-stoichiometric BN layers are obtained. Their structure in terms of crystallinity can be adjusted from amorphous to well-crystalline sp2 phase by controlling the treatment temperature. In particular, a crystallization onset occurs at 1000 °C and well defined sp2 crystalline planes oriented parallel to the surface are noted after ceramization at 1350 °C. Finally, side-modification of the substrate surface induced by the thermal treatment appears to impact on the final BN topography and defect generation.

Low-resistivity molybdenum-carbide thin films formed by thermal atomic layer deposition with pressure-assisted decomposition reaction

The rapid increase in the resistivity of thin metal films as their thickness decreases to sub-10 nm, known as the resistivity size effect, is an important issue that must be addressed to ensure device performance in ultraminiaturized semiconductor devices. Molybdenum carbide (MoCx) has been studied as a candidate for emerging interconnection materials because it can maintain a low resistivity even at a low thickness. However, reports on stable precursors with guaranteed reactivity for atomic layer deposition (ALD) remain limited; moreover, the process of forming low-resistance MoCx thin films must be studied. In this study, we propose a new route to form low-resistivity MoCx thin films by thermal ALD with partial ligand dissociation by controlling the process pressure to enhance the reactivity of the Mo precursor with reactants. Following the proposed deposition process and subsequent annealing, uniform and continuous thin films were formed (even at a sub-5 nm thickness), with an extremely low resistivity of approximately 130 μΩ cm. Therefore, the proposed method can be applied as a next-generation interconnect process; notably, high-quality thin films can be formed through pressure-assisted decomposition, even with a lack of thermal energy during the ALD process.

Improved Ga2O3 films on variously oriented Si substrates with Al2O3 or HfO2 buffer layer via atomic layer deposition

Ga2O3 is an ultrawide-band-gap semiconductor with excellent properties and promising applications in the electronic and optoelectronics. For acting as the substrate for heteroepitaxial Ga2O3 films, Si has the advantages of wafer-level size, cheap price and nice compatibility whereas also perform the disadvantage of large thermal mismatch. In this paper, the apparent flower-like defects are exhibited on the macroscopic surfaces of annealed Ga2O3 films deposited on (100), (110) and (111) oriented Si substrates by atomic layer deposition (ALD) method. The reason is ascribed to the different thermal expansion coefficients between Ga2O3 and Si induced compressive and tensile stresses. The Al2O3 or HfO2 buffer layer intercalated between Ga2O3 films and Si substrates via successive ALD process suppress the flower-like defects effectively while the surface roughnesses are low to be 1.290 nm and 2.393 nm, respectively. XRD spectra demonstrate that buffer layer indeed relieves the stress of Ga2O3 films on Si substrates while the amorphous Al2O3 has better influence than the polycrystalline HfO2. The results are helpful to the improvement of growth quality and device property of Ga2O3.

Remarkable Bias‐Stress Stability of Ultrathin Atomic‐Layer‐Deposited Indium Oxide Thin‐Film Transistors Enabled by Plasma Fluorination

AbstractA low‐thermal‐budget fabrication approach is developed to realize high‐performance fluorine‐doped indium oxide (In2O3:F) thin‐film transistors (TFTs) with remarkable bias‐stress stability. The ultrathin transistor channel layer is prepared by a re‐developed atomic layer deposition (ALD) process of using cyclopentadienyl indium(I) (InCp) and O2 plasma to deposit a crystalline In2O3 film, followed by a new fluorine doping strategy to use CF4 plasma to afford the In2O3:F layer. As revealed by the density functional theory (DFT) analysis, the fluorine doping can stabilize the lattice oxygen and electrically passivate the problematic VO defects in In2O3 by forming the FOFi spectator defects. Therefore, the fabricated In2O3:F TFTs show simultaneously excellent electrical performance and remarkable bias‐stress stability, with high µFE of 35.9 cm2 V−1 s−1, positive Vth of 0.36 V, steep SS of 94.3 mV dec−1, small hysteresis of 33 mV, and small ΔVth of −111 and 49 mV under NBS and PBS, respectively. This work demonstrates the high promise of the fluorinated ALD In2O3:F TFTs for the CMOS back‐end‐of‐line (BEOL) compatible technologies toward advanced monolithic 3D integration.

Interface-Engineered Atomic Layer Deposition of 3D Li4Ti5O12 for High-Capacity Lithium-Ion 3D Thin-Film Batteries.

Upcoming energy-autonomous mm-scale Internet-of-things devices require high-energy and high-power microbatteries. On-chip 3D thin-film batteries (TFBs) are the most promising option but lack high-rate anode materials. Here, Li4Ti5O12 thin films fabricated by atomic layer deposition (ALD) are electrochemically evaluated on 3D substrates for the first time. The 3D Li4Ti5O12 reveals an excellent footprint capacity of 20.23µAhcm-2 at 1 C. The outstanding high-rate capability is demonstrated with 7.75µAhcm-2 at 5mAcm-2 (250 C) while preserving a remarkable capacity retention of 97.4% after 500 cycles. Planar films with various thicknesses exhibit electrochemical nanoscale effects and are tuned to maximize performance. The developed ALD process enables conformal high-quality spinel (111)-textured Li4Ti5O12 films on Si substrates with an area enhancement of 9. Interface engineering by employing ultrathin AlOx on the current collector facilitates a required crystallization time reduction which ensures high film and interface quality and prospective on-chip integration. This work demonstrates that 3D Li4Ti5O12 by ALD can be an attractive solution for the microelectronics-compatible fabrication of scalable high-energy and high-power Li-ion 3D TFBs.

Fabrication of humidity monitoring sensor using porous silicon nitride structures for alkaline conditions

Porous silicon nitride structures were fabricated for a humidity sensor. The porous silicon structures were fabricated by the metal-assisted chemical etching process, and the conformal silicon nitride thin film was deposited by the atomic layer deposition process. The optimized porous sensor with the 10 nm-thick silicon nitride thin film had a hydrophilic surface and compared to other sensors, had an excellent humidity sensing response. Especially, it showed a superior humidity sensing response at 1 kHz with fast response and recovery times of 13.3 s and 12.4 s, respectively, were observed. Based on the electrochemical impedance spectroscopy results, the equivalent circuits and humidity sensing mechanism were discussed. The chemical stability of the silicon nitride was characterized using Tafel analysis in alkaline electrolytes. Additionally, the sensor's humidity sensing capabilities were tested under cement-embedded conditions.

Crystalline as-deposited TiO 2 anatase thin films grown from TDMAT and water using thermal atomic layer deposition with in situ layer-by-layer air annealing

We report a new thermal atomic layer deposition (thermal-ALD) process including an air exposure as a third precursor to deposit crystalline TiO2 anatase thin films from tetrakis(dimethylamido)titanium(IV) (TDMAT) and water at deposition temperatures as low as 180 °C and film thicknesses as low as 10 nm. This ALD process enables TiO2-antase crystal growth during the deposition at low temperatures (< 220 °C). This additional oxidant pulse is used to fully oxidize the Ti to a 4+ state in the amorphous film, lowering the barrier to crystalline anatase formation. This new approach is informed by preliminary studies of post-deposition annealing (PDA) of thermal ALD films in both nitrogen and air atmospheres, which demonstrate the importance of having an oxidizing atmosphere to achieve the nucleation of the crystalline anatase phase. This oxidizing atmosphere is subsequently introduced into the ALD cycle as a third precursor and is shown to be more effective and efficient in promoting the crystalline transformation than even by post-deposition annealing. The crystalline anatase phase is verified by Raman spectroscopy and grazing incidence X-ray diffraction (GIXRD). The mechanism for crystallization during the TDMAT/H2O/air ALD cycle is probed by chemical state analysis via X-ray photoelectron spectroscopy (XPS). We propose that sub-oxidation in TiO2 thin films deposited by the thermal-ALD process inhibits crystallization during ALD from TDMAT/H2O chemistry. Scanning electron microscopy (SEM) is used to investigate the microstructure of these TiO2 thin films as a function of thickness (5 nm to 50 nm) and deposition temperature (180 °C to 220 °C). The reported layer-by-layer air anneal process is found to crystallize entire films in shorter total process times than thermal-ALD with ex situ post deposition annealing at identical temperatures, presumably due to the improved surface diffusion kinetics accessed during the deposition process.

Chemisorption of tetrakis(dimethylamino)zirconium on zirconium oxide: Density functional theory study

We investigated the chemisorption mechanism of tetrakis(dimethylamino)zirconium, Zr(NMe2)4, on zirconium oxide (ZrO2) to understand the first half-reaction of the atomic layer deposition (ALD) process of ZrO2 films. A hydroxylated monoclinic ZrO2 (-111) 2×2 slab model was constructed, and the surface hydroxyl group density was optimized. The obtained density through the optimization procedure was 4.5 nm−2, which closely matches the value reported in the literature. Then, the sequential ligand exchange reactions involving a Zr(NMe2)4 molecule and the –OH terminated ZrO2 surface were simulated. The first two reactions had low activation energies of 0.19 and 0.24 eV and were exothermic. Conversely, the third reaction was endothermic. Therefore, the resulting surface species after chemisorption was expected to be O2Zr(NMe2)2*, which is consistent with in situ analyses in the literature.

Tailoring indium oxide film characteristics through oxygen reactants in atomic layer deposition with highly reactive liquid precursor

Indium oxide (InOx) films were deposited via atomic layer deposition (ALD) using a novel liquid indium precursor, dimethyl[N1-(tert-butyl)–N2,N2-dimethylethane-1,2-diamine]indium (DMITN). In this process, the reactant (H2O, O3, or O2 plasma) and substrate temperature (100–250 ℃) were varied. The DMITN precursor showed excellent reactivity with all three reactants. The growth characteristics (ALD window, growth per cycle, and step coverage) and film properties (impurities, stoichiometry, oxygen bonding state, crystallinity, film density, and electrical properties) differed based on the ALD process employed, ascribed to the distinct thermal energies and inherent reactivities of the chosen oxidants. As the oxidation energy of the reactants increased (H2O < O3 < O2 plasma), the growth per cycle (GPC) and the oxygen–indium bond ratio of InOx increased. Crystallinity analysis also revealed significant differences depending on the reactants, where the Hall mobility was predominantly influenced by the crystal alignment. The step coverage at an aspect ratio of 40:1 was markedly superior with the use of H2O and O3 reactants (approximately 95 %) compared to that with O2 plasma (approximately 74 %). These findings highlight the capability of controlling the growth and properties of InOx films by judiciously selecting the reactant, emphasizing the versatility of the DMITN precursor in ALD processes.

Preparation of palladium-based catalyst by plasma-assisted atomic layer deposition and its applications in CO2 hydrogenation reduction

Supported Pd catalyst is an important noble metal material in recent years due to its high catalytic performance in CO2 hydrogenation. A fluidized-bed plasma assisted atomic layer deposition (FP-ALD) process is reported to fabricate Pd nanoparticle catalyst over γ-Al2O3 or Fe2O3/γ-Al2O3 support, using palladium hexafluoroacetylacetonate as the Pd precursor and H2 plasma as counter-reactant. Scanning transmission electron microscopy exhibits that high-density Pd nanoparticles are uniformly dispersed over Fe2O3/γ-Al2O3 support with an average diameter of 4.4 nm. The deposited Pd-Fe2O3/γ-Al2O3 shows excellent catalytic performance for CO2 hydrogenation in a dielectric barrier discharge reactor. Under a typical condition of H2 to CO2 ratio of 4 in the feed gas, the discharge power of 19.6 W, and gas hourly space velocity of 10000 h−1, the conversion of CO2 is as high as 16.3% with CH3OH and CH4 selectivities of 26.5% and 3.9%, respectively.

Enhancing Carbon Fiber Fabrics with ALD AlxOy Coatings: An Investigation of Thickness Effects on Weight, Morphology, Coloration, and Thermal Properties

This study explores the impact of non-stoichiometric aluminum oxide (AlxOy) coatings applied via thermal atomic layer deposition (ALD) on carbon fiber fabrics (CFFs), emphasizing volume per cycle, FESEM analyses, color transitions, and thermal stability enhancements. Using trimethylaluminum and water at 100 °C, AlxOy was deposited across a range of 1000 to 5000 ALD cycles, with film thicknesses extending up to 500 nm. This notable increase in the volume of material deposited per cycle was observed for the 3D CFFs, highlighting ALD’s capability to coat complex structures effectively. FESEM analyses revealed the morphological evolution of CFF surfaces post-coating, showing a transition from individual grains to a dense, continuous layer as ALD cycles increased. This morphological transformation led to significant color shifts from green to red to blue, attributed to structural coloration effects arising from variations in film thickness and surface morphology. Thermogravimetric analyses (TGA and dTG) indicated that the AlxOy coatings enhanced the thermal stability of CFFs, with a postponement in degradation onset observed in samples subjected to more ALD cycles. In essence, this research highlights the nuanced relationship between ALD processing parameters and their collective influence on both the aesthetic and functional properties of CFFs. This study illustrates ALD’s potential in customizing CFFs for applications requiring specific color and thermal resilience, balancing the discussion between the surface morphological changes and their implications for color and thermal behavior.

Exploring TMA and H2O Flow Rate Effects on Al2O3 Thin Film Deposition by Thermal ALD: Insights from Zero-Dimensional Modeling

This study investigates the impact of vapour-phase precursor flow rates—specifically those of trimethylaluminum (TMA) and deionized water (H2O)—on the deposition of aluminum oxide (Al2O3) thin films through atomic layer deposition (ALD). It explores how these flow rates influence film growth kinetics and surface reactions, which are critical components of the ALD process. The research combines experimental techniques with a zero-dimensional theoretical model, designed specifically to simulate the deposition dynamics. This model integrates factors such as surface reactions and gas partial pressures within the ALD chamber. Experimentally, Al2O3 films were deposited at varied TMA and H2O flow rates, with system conductance guiding these rates across different temperature settings. Film properties were rigorously assessed using optical reflectance methods and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The experimental findings revealed a pronounced correlation between precursor flow rates and film growth. Specifically, at 150 °C, film thickness reached saturation at a TMA flow rate of 60 sccm, while at 200 °C, thickness peaked and then declined with increasing TMA flow above this rate. Notably, higher temperatures generally resulted in thinner films due to increased desorption rates, whereas higher water flow rates consistently produced thicker films, emphasizing the critical role of water vapour in facilitating surface reactions. This integrative approach not only deepens the understanding of deposition mechanics, particularly highlighting how variations in precursor flow rates distinctly affect the process, but also significantly advances operational parameters for ALD. These insights are invaluable for enhancing the application of ALD technologies across diverse sectors, including microelectronics, photovoltaics, and biomedical coatings, effectively bridging the gap between theoretical predictions and empirical results.

Self-Induced Ge-Doped HfO2 Applied to Ge Stacked Nanowires Ferroelectric Gate-All-Around Field-Effect Transistor with Steep Subthreshold Slope Under O3 Treatment with GeO2 as Interfacial Layer

This study reports a self-induced ferroelectric Ge-doped HfO2 (Ge:HfO2) thin film through interface reactions. In the first experiment, three treatments for forming interfacial layer (IL) were discussed through TiN/2-nm-thick Al2O3/2-nm-thick Ge:HfO2/GeO2/Ge metal-ferroelectric-insulator-semiconductor capacitors. The remnant polarization (Pr), leakage current, and interface trap density (Dit) were compared to select the most appropriate IL treatment. The results show that the in-situ ozone treatment under the standard atomic layer deposition process had the second highest 2Pr value as well as lower Dit values. Next, the thicknesses of Al2O3/Ge:HfO2 would be changed to 4 nm/2 nm and 3 nm/3 nm to investigate the ferroelectricity and leakage current. Although the 3-nm-thick Al2O3/3-nm-thick Ge:HfO2 shows a lower 2Pr value, the leakage current is much lower than 2-nm-thick Al2O3/2-nm-thick Ge:HfO2. The self-induced ferroelectric 3-nm-thick Ge:HfO2 thin film was then applied to fabricate Ge stacked nanowires gate-all-around field-effect transistor. The results show a steep subthreshold slope of 58 mV/dec for pFET and on-off current ratio > 105 and have high potential in low-power IC applications.

Simultaneous Band Alignment Modulation and Carrier Dynamics Optimization Enable Highest Efficiency in Cd‐Free Sb2Se3 Solar Cells

AbstractAntimony selenide (Sb2Se3) has developed as an eco‐friendly photovoltaic candidate owing to its non‐toxic composition and exceptional optoelectronic properties. However, the toxic and parasitic light‐absorbing CdS are widely used as electron transport layer (ETL) in Sb2Se3 solar cells, which severely limits its development. Herein, an alternative, zinc tin oxide (ZTO) ETL with varying composition‐dependent energy structure is deposited by atomic layer deposition (ALD) technique and used for constructing Cd‐free Sb2Se3 solar cells. It has been found that the ZTO ETL possessing an appropriate Zn/Sn ratio can alter the Sb2Se3/ZTO heterojunction band alignment to an ideal “spike‐like” arrangement. It not only suppresses the accumulation and recombination of charge carriers at the interface, but also effectively enhances carrier transport. In addition, thanks to the formation of passivated Sb2O3 ultra‐thin layer upon ALD process, the non‐radiative recombination within bulk Sb2Se3 can be effectively suppressed, and therefore enhancing carrier lifetime, extraction efficiency, and collection efficiency. Consequently, the as‐fabricated Mo/Sb2Se3/ZTO/ITO/Ag thin‐film solar cell demonstrates an impressive efficiency of 8.63%. This accomplishment establishes it as the most efficient Cd‐free Sb2Se3 solar cell to date, underscoring the significant advantages of incorporating ZTO ETL in the development of Sb2Se3 photovoltaic scenarios.

Generation and Applications of a Broad Atomic Oxygen Beam with a High Flux‐Density via Collision‐Induced Dissociation of O2

Generation and Applications of a Broad Atomic Oxygen Beam with a High <scp>Flux‐Density</scp> via <scp>Collision‐Induced</scp> Dissociation of <scp>O₂</scp>

Plasma enhanced atomic layer deposition of silicon nitride using magnetized very high frequency plasma

To obtain high-quality SiN x films applicable to an extensive range of processes, such as gate spacers in fin field-effect transistors (FinFETs), the self-aligned quadruple patterning process, etc, a study of plasma with higher plasma density and lower plasma damage is crucial in addition to study on novel precursors for SiN x plasma-enhanced atomic layer deposition (PEALD) processes. In this study, a novel magnetized PEALD process was developed for depositing high-quality SiN x films using di(isopropylamino)silane (DIPAS) and magnetized N2 plasma at a low substrate temperature of 200 °C. The properties of the deposited SiN x films were analyzed and compared with those obtained by the PEALD process using a non-magnetized N2 plasma source under the same conditions. The PEALD SiN x film, produced using an external magnetic field (ranging from 0 to 100 G) during the plasma exposure step, exhibited a higher growth rate (∼1 Å/cycle) due to the increased plasma density. Additionally, it showed lower surface roughness, higher film density, and enhanced wet etch resistance compared to films deposited using the PEALD process with non-magnetized plasmas. This improvement can be attributed to the higher ion flux and lower ion energy of the magnetized plasma. The electrical characteristics, such as interface trap density and breakdown voltage, were also enhanced when the magnetized plasma was used for the PEALD process. Furthermore, when SiN x films were deposited on high-aspect-ratio (30:1) trench patterns using the magnetized PEALD process, an improved step coverage of over 98% was achieved, in contrast to the conformality of SiN x deposited using non-magnetized plasma. This enhancement is possibly a result of deeper radical penetration enabled by the magnetized plasma.

Infrared Imaging Using Thermally Stable HgTe/CdS Nanocrystals.

Transferring nanocrystals (NCs) from the laboratory environment toward practical applications has raised new challenges. HgTe appears as the most spectrally tunable infrared colloidal platform. Its low-temperature synthesis reduces the growth energy cost yet also favors sintering. Once coupled to a read-out circuit, the Joule effect aggregates the particles, leading to a poorly defined optical edge and large dark current. Here, we demonstrate that CdS shells bring the expected thermal stability (no redshift upon annealing, reduced tendency to form amalgams, and preservation of photoconduction after an atomic layer deposition process). The electronic structure of these confined particles is unveiled using k.p self-consistent simulations showing a significant exciton binding energy of ∼200 meV. After shelling, the material displays a p-type behavior that favors the generation of photoconductive gain. The latter is then used to increase the external quantum efficiency of an infrared imager, which now reaches 40% while presenting long-term stability.

Catalytic atomic layer deposition of amorphous alumina–silica thin films on carbon microfibers

Deposition of silica-based thin films on carbon microfibers has long been considered a challenge. Indeed, the oxidation-sensitive nature of carbon microfibers over 550 K and their submicron-textured surface does not bode well with the required conformity of deposition best obtained by atomic layer deposition (ALD) and the thermal oxidative conditions associated with common protocols of silica ALD. Nonetheless, the use of a catalytic ALD process allowed for the deposition of amorphous alumina–silica bilayers from 445 K using trimethylaluminium and tris(tert-pentoxy)silanol (TPS). In this study, first undertaken on flat silicon wafers to make use of optical spectroscopies, the interplay between kinetics leading to a dense silica film growth was investigated in relation to the applied operation parameters. A threshold between the film catalyzed growth and the complete outgassing of pentoxy-derived compounds from TPS was found, resulting in a deposition of equivalent growth per cycle of 1.1 nm c−1, at a common ALD rate of 0.3 nm min−1, with a flat thickness gradient. The deposition on carbon microfiber fabrics was found conformal, albeit with a thickness growth capped below 20 nm, imparted by the microfiber surface texture. STEM-EDX showed a sharp interface of the bilayer with limited carbon diffusion. The conformal and dense deposition of alumina–silica thin films on carbon microfibers holds great potential for further use as refractory oxygen barrier layers.

Remote inductively coupled plasmas in Ar/N2 mixtures and implications for plasma enhanced ALD

Plasma enhanced atomic layer deposition (PEALD) is a cyclic atomic layer deposition (ALD) process that incorporates plasma-generated species into one of the cycle substeps. The addition of plasma is advantageous as it generally provides unique reactants and a substantially reduced growth temperature compared to thermal approaches. However, the inclusion of plasma, coupled with the increasing variety of plasma sources used in PEALD, can make these systems challenging to understand and control. This work focuses on the use of plasma diagnostics to examine the plasma characteristics of a remote inductively coupled plasma (ICP) source, a type of plasma source that is commonly used for PEALD. Ultraviolet to near-infrared spectroscopy and spatially resolved Langmuir probe measurements are employed to characterize a remote ICP system using nitrogen-based gas chemistries typical for III-nitride growth processes. Spectroscopy is used to characterize the relative concentrations of important reactive and energetic neutral species generated in the remote ICP as a function of gas flow rate, Ar/N2 flow fraction, and gas pressure. In addition, the plasma potential and plasma density for the same process parameters are examined using an RF compensated Langmuir probe downstream from the ICP source. The results are also discussed in terms of their impact on materials growth.

Controllable surface functionalization of rice husk-derived porous carbon by atomic layer deposition for highly-efficient microwave absorption

Multilayer absorbers, characterized by their distinctive structures and numerous heterogeneous interfaces, possess the potential to become exceptionally efficient and stable electromagnetic wave absorbers. Herein, we have ingeniously engineered multilayer ZnO/NiCo/C (ZNC) composite absorbers, utilizing a combination of an annealing procedure and atomic layer deposition (ALD) process. From the SEM images, the ZnO layers composed of ZnO nanoparticles (NPs) fabricated via ALD almost completely cover the surface of rice husk-derived carbon and the NiCo NPs residing on the surface. Benefiting from the specific multilayer structure, the well-designed ternary dielectric/magnetic components, and the synergistic interplay between dipole polarization relaxation and interfacial polarization relaxation, coupled with good impedance matching, the ZNC150 and ZNC200 composites exhibit best microwave absorption capacities. Through the precise control of the electromagnetic parameters by the deposition circle modifications, the minimum reflection loss reaches −52.5 dB and the effective bandwidth extends to 4.96 GHz with thin thickness of 1.52 mm.