Nitride‐based surface acoustic wave devices and applications

Abstract

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

Sub-optical wavelength acoustic wave modulation of integrated photonic resonators at microwave frequencies

“…In Fig. 2c, k 2 31,32 . However, when L is reduced to below 1 mm, k 2 decreases dramatically, making the fundamental mode more difficult to be excited as observed in Fig.…”

Surface acoustic waves in semi-insulating Fe-doped GaN films grown by hydride vapor phase epitaxy

“…GaN as a wide band gap semiconductor is a promising material for SAW devices which may be capable of integrating with electronic or optoelectronic functions in one chip and operating in harsh environments. [1][2][3][4][5] So far, many works have been done focusing on the fundamental properties of SAW in GaN films, including the propagation properties, the dispersion of SAW velocities, and the electromechanical coupling coefficients. [6][7][8][9][10][11][12][13] In these studies, the thickness and the resistivity of the GaN films were assumed to be key factors to affect the surface acoustic modes and the electromechanical coupling coefficients.…”

Simulation of dynamic characteristics of GaN p-i-n avalanche diode operating as particle detector with internal gain

“…Recent advances in semiconductor technology are attained due to intensive investigations and wide applications of gallium nitride (GaN) based semiconductor devices, such as light emitting diodes [1,2] and lasers [3,4], photodiodes [5,6], HEMTs [7,8], surface acoustic wave sensors [9] and acous to-optic devices [10,11]. Gallium nitride is one of the most promising materials for fabrication of particle detectors operating within a harsh radiation environment [12][13][14][15][16][17][18], based on small dark as well as leakage currents and high breakdown voltages.…”