GaN-based SAW delay-line oscillator

Čiplys, D.; Rimeika, R.; Sereika, A.; Gaška, R.; Shur, M. S.; Yang, Jinwei; Khan, M. Asif

doi:10.1049/el:20010358

Cited by 44 publications

(15 citation statements)

References 3 publications

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“…Two different UV sensors based on nitrides have been reported, in which light incides on the region between transducers. The first device is a delay line oscillator, whose frequency down-shifts under UV illumination [35]. This shift, which increases with illumination density, is due to a change in velocity by UV via screening the piezoelectric fields by photoconductivity.…”

Section: Saw-assisted Uv Sensorsmentioning

confidence: 99%

Nitride‐based surface acoustic wave devices and applications

Calle

Pedrós

Palacios

et al. 2005

phys. stat. sol. (c)

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A review of the fabrication techniques of surface acoustic wave (SAW) devices in nitrides, and their most relevant device properties, is presented. Several acoustic modes are observed in the transfer functions of the filters: besides the Rayleigh wave, guided modes (Sezawa) arise when the sound velocity in the nitride layer is lower than in the substrate, and pseudobulk modes may also appear. The effect of the substrate characteristics will be addressed, including the anisotropy found in nitride devices grown on sapphire due to the crystal structure mismatch. Regarding applications, some results in the sensor and photonics fields are summarized. Finally, two novel devices will be discussed: a SAW-assisted photodetector, based on the integration of a SAW generator and a UV photodetector, and a DC controlled SAW filter, obtained by the fabrication of a SAW device on a 2DEG AlGaN/GaN heterostructure.1 Introduction Surface acoustic wave (SAW) devices are a convenient solution for high frequency filters in mobile communication systems due to their stability, reliability and compactness [1]. SAW devices are also ideal for gas sensing, with industrial, environmental and biomedical applications [2,3]. Furthermore, SAW sensors offer the additional feature of wireless transmission, and therefore the feasibility of operation in harsh environments [4,5]. Whereas acoustic wave devices are typically fabricated on quartz or LiNbO 3 , other materials where devices exhibit novel or improved characteristics are highly desired. Thin-film piezoelectric semiconductors offer the potential for integration and compatibility with the electromechanical systems and electronic technologies. In particular, III-nitrides, specially AlN, combine high SAW velocity and electromechanical coupling coefficients, while showing excellent thermal stability. The device operation frequency can be increased either by reducing the device patterns or by using substrates with high sound velocity. These properties pave the way for the development of SAW devices operating in the GHz range. Moreover, the interaction of surface waves with electrons and photons, together with the direct bandgap of AlGaN, opens a wide window for new applications in micro and optoelectronics.A brief introduction to propagation of acoustic waves in nitride films is given in Sect. 2. Several acoustic modes are observed in the transfer functions: Rayleigh wave, guided modes when the sound is slower in the nitride layer than in the substrate (e.g., GaN/sapphire or AlN/diamond), and pseudobulk modes. On the other hand, anisotropic propagation is found when using sapphire substrates, due to the crystal structure mismatch. A review of the fabrication techniques of nitrides SAW devices, and their characterization, will be summarized in Sect. 3. Finally, Sect. 4 is devoted to applications of nitride SAW devices; among them, two novel devices will be described: a SAW-assisted photodetector, based on the

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Section: Saw-assisted Uv Sensorsmentioning

confidence: 99%

Nitride‐based surface acoustic wave devices and applications

Calle

Pedrós

Palacios

et al. 2005

phys. stat. sol. (c)

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“…4,6,8 It has been reported that the device characteristics of GaN-based transversal filters are sensitive to ultraviolet illumination. 12,13 Recently, Grajal et al 14 showed that the insertion loss of transversal filters fabricated on AlGaN/ GaN heterostructures changes when dc bias voltages are applied to their interdigital transducers ͑IDTs͒.…”

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Side-gate effects on transfer characteristics in GaN-based transversal filters

Shigekawa

Nishimura

Yokoyama

et al. 2005

Applied Physics Letters

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We examine the transfer characteristics of transversal filters with side gates fabricated on unintentionally doped GaN layers grown on (0001) sapphire substrates. By positively biasing the side gates, the transfer characteristics of the filters are efficiently improved, which means that GaN-based transversal filters with side gates are potentially applicable for filtering and modulating rf signals. We further examine the capacitance in an interdigital transducer, which decreases when the side-gate bias voltage increases. This indicates that the variation in the transfer characteristics is likely to be attributable to a change in the depletion-layer thickness in the GaN layers.

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“…[4] from measurements of the SAW velocity on a free and metallized surface. It should be noted, however, that the latter method may lead to the overestimation of the electromechanical coupling coefficient due to the additional contribution from the mass loading of the wave propagation surface by the deposited film [8].…”

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confidence: 99%

Electromechanical Coupling Coefficient for Surface Acoustic Waves in GaN-on-Sapphire

Rimeika

Čiplys

Shur

et al. 2002

phys. stat. sol. (b)

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The electromechanical coupling coefficient for surface acoustic waves propagating in GaN-on-sapphire structure has been evaluated using in situ measurements of the SAW attenuation during the evaporation of a metal film on the GaN surface. The extracted values for samples with GaN layer thicknesses of 2.2-2.4 mm were in the range of 0.06-0.09% at SAW frequencies of 200-300 MHz.Introduction Surface acoustic waves (SAWs) have found important applications in material research, signal processing, and telecommunications areas. There is a considerable interest in SAW investigations in thin-film structures based on GaN family of semiconductors. The key parameter for SAW devices is the electromechanical coupling coefficient, K 2 . The efficiency of the SAW interdigital transducer (IDT) is characterized by its radiation conductance G a ðf 0 Þ ¼ 8K 2 f 0 C T N at center frequency f 0 , where C T is the IDT static capacitance and N is the number of the IDT electrode pairs. The electromechanical coupling coefficient for SAWs can be expressed as K 2 ¼ 2DV=V, where DV is the magnitude of the SAW velocity change that occurs when the free surface of the piezoelectric is shorted by a thin highly conducting metal film, and V is the unperturbed SAW velocity. The K 2 values for SAWs in GaN-on-sapphire structures have been evaluated from transducer performance analysis and extracted from the velocity measurements by several authors [1][2][3][4]. However, there is a considerable disagreement in the results, and further investigations are necessary. For this purpose, we have chosen the technique, different from those mentioned above. We report on the evaluation of the electromechanical coupling coefficient for GaNon-sapphire structures using in situ measurements of the SAW attenuation during the evaporation of a metal film on the surface of the piezoelectric [5,6].

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GaN-based SAW delay-line oscillator

Cited by 44 publications

References 3 publications

Nitride‐based surface acoustic wave devices and applications

Nitride‐based surface acoustic wave devices and applications

Side-gate effects on transfer characteristics in GaN-based transversal filters

Electromechanical Coupling Coefficient for Surface Acoustic Waves in GaN-on-Sapphire

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