Effect of negative ions generation from sputtering target on crystalline orientation and k<sub>t</sub>
                  <sup>2</sup> of ScAlN thin films

Kihara, Rui; Takayanagi, Shinji; Yanagitani, Takahiko

doi:10.1109/ultsym.2019.8925983

Cited by 3 publications

(3 citation statements)

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“…ScAlN films lose piezoelectricity above a Sc concentration of 43% because the crystal structure of the ScAlN film changes from wurtzite to rocksalt. However, it has been reported that the piezoelectric properties of the films can deteriorate before the Sc concentration reaches 43% without an isostructural phase transition, which is a serious problem [21][22][23]. One cause of this phenomenon is negative-ion bombardment of the substrate during sputtering deposition.…”

Section: Introductionmentioning

confidence: 99%

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Negative-ion bombardment increases during low-pressure sputtering deposition and their effects on the crystallinities and piezoelectric properties of scandium aluminum nitride films

Tominaga¹,

Takayanagi²,

Yanagitani³

2021

J. Phys. D: Appl. Phys.

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Scandium aluminum nitride (ScAlN) films are being actively researched to explore their potential for use in bulk acoustic wave (BAW) and surface acoustic wave (SAW) resonators because of their good piezoelectric properties. Sputtering is commonly used in ScAlN film deposition. Unfortunately, it has been reported that film quality metrics such as the crystallinity and piezoelectric properties can deteriorate before the Sc concentration reaches 43% without an isostructural phase transition. One reason for this is bombardment with negative ions generated from carbon and oxygen impurities in the Sc ingots. Because the number of negative ions increases during low-pressure sputtering deposition, their effect on film quality may be considerable. In this study, we investigated negative-ion bombardment of the substrate during sputtering deposition and its effects on ScAlN crystallinity and piezoelectric properties. Negative-ion energy distribution measurements indicated that many more negative ions collide with the substrate during ScAlN film deposition than during AlN deposition. In addition, decreasing the sputtering pressure further increased the number of negative ions and their energies. It is well known that film quality improves at low pressures because increasing the mean free path reduces thermalization and scattering of sputtered particles. Although, AlN crystallinity and piezoelectric properties improved at low pressures, the properties of ScAlN films deteriorated dramatically. Therefore, the results indicated that ion bombardment increase at low pressure adversely effects ScAlN crystal growth, deteriorating crystallinity and piezoelectric properties. ScAlN films may be improved further by suppressing negative-ion bombardment of the substrate.

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Section: Introductionmentioning

confidence: 99%

“…Then, they are accelerated in the electric field near the target and collide with the substrate on which the sputtered particles are depositing. This deteriorates film quality characteristics such as the crystallinity and piezoelectric properties [21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Negative-ion bombardment increases during low-pressure sputtering deposition and their effects on the crystallinities and piezoelectric properties of scandium aluminum nitride films

Tominaga¹,

Takayanagi²,

Yanagitani³

2021

J. Phys. D: Appl. Phys.

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“…Recently, AlN thin film has got much attention because it has higher phase velocity (over 5000 m/s) compared to other piezoelectric thin films. [22][23][24][25][26][27][28][29] Moreover, it can be deposited on substrates with high phase velocity, such as diamond and SiC, resulting a great candidate for high frequency SAW devices. [30][31][32] The frequency of the device based on AlN/diamond structure reached 5 GHz [33], while a Sezawa wave filter based on ZnO/SiC structure with the center frequency of 6.8 GHz was prepared successfully in our previous work [34].…”

Section: Introductionmentioning

confidence: 99%

3D Layout of Interdigital Transducers for High Frequency Surface Acoustic Wave Devices

Shen

Luo

et al. 2020

IEEE Access

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The development of mobile communication sets higher demands on high frequency surface acoustic wave (SAW) devices. The layout of interdigital transducers (IDT) in SAW devices is in plane and the traditional methods of improving frequency for SAW devices are the increase of acoustic velocity and the reduction of wavelength. However, these methods have a limit due to the limited acoustic velocity and the photolithography limit. This work proposes a new way for the development of high frequency SAW devices by redesigning the layout of IDT in three dimensions (3D). The set of IDTs is split into two layers, i.e. the ground electrodes on one layer and the signal electrodes on the other layer. This 3D layout of IDTs dramatically narrows the horizontal gap between two adjacent electrodes, which can significantly increase the frequency. The frequency and the electromechanical coupling factor (K 2) of the four structures of SAW devices with the 3D layout of IDTs were studied by the finite element method (FEM). The results show that the frequency can be doubled under the same critical resolution of lithography due to the shortening of wavelength, and the 3D layout of IDTs is available for SAW devices based on piezoelectric thin film or piezoelectric single crystal. This work develops a new alternative to increase the working frequency of SAW devices.

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Deterioration in the piezoelectric property of ScAlN thin films by negative ion bombardment increased in low-pressure sputtering deposition

Tominaga

Takayanagi

Yanagitani

2020

2020 IEEE International Ultrasonics Symposium (IUS)

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Effect of negative ions generation from sputtering target on crystalline orientation and k_t ² of ScAlN thin films

Cited by 3 publications

References 3 publications

Negative-ion bombardment increases during low-pressure sputtering deposition and their effects on the crystallinities and piezoelectric properties of scandium aluminum nitride films

Negative-ion bombardment increases during low-pressure sputtering deposition and their effects on the crystallinities and piezoelectric properties of scandium aluminum nitride films

3D Layout of Interdigital Transducers for High Frequency Surface Acoustic Wave Devices

Deterioration in the piezoelectric property of ScAlN thin films by negative ion bombardment increased in low-pressure sputtering deposition

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Effect of negative ions generation from sputtering target on crystalline orientation and kt 2 of ScAlN thin films

Cited by 3 publications

References 3 publications

Negative-ion bombardment increases during low-pressure sputtering deposition and their effects on the crystallinities and piezoelectric properties of scandium aluminum nitride films

Negative-ion bombardment increases during low-pressure sputtering deposition and their effects on the crystallinities and piezoelectric properties of scandium aluminum nitride films

3D Layout of Interdigital Transducers for High Frequency Surface Acoustic Wave Devices

Deterioration in the piezoelectric property of ScAlN thin films by negative ion bombardment increased in low-pressure sputtering deposition

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Effect of negative ions generation from sputtering target on crystalline orientation and k_t ² of ScAlN thin films