In this paper, an AIN/free-standing nanocrystalline diamond (NCD) system is proposed in order to process high frequency surface acoustic wave (SAW) resonators for sensing applications. The main problem of synthetic diamond is its high surface roughness that worsens the sputtered AIN quality and hence the device response. In order to study the feasibility of this structure, AIN films from 150 nm up to 1200 nm thick have been deposited on free-standing NCD. We have then analysed the influence of the AIN layer thickness on its crystal quality and device response. Optimized thin films of 300 nm have been used to fabricate of one-port SAW resonators operating in the 10-14 GHz frequency range. A SAW based sensor pressure with a sensibility of 0.33 MHz/bar has been fabricated.

Abstract-This letter describes the procedure to manufacture high-performance surface acoustic wave (SAW) resonators on AlN/diamond heterostructures working at frequencies beyond 10 GHz. In the design of SAW devices on AlN/diamond systems, the thickness of the piezoelectric layer is a key parameter. The influence of the film thickness on the SAW device response has been studied. Optimized thin films combined with advanced e-beam lithographic techniques have allowed the fabrication of one-port SAW resonators with finger width and pitch of 200 nm operating in the 10-14 GHz range with up to 36 dB out-of-band rejection.Index Terms-AlN/diamond, surface acoustic wave (SAW) resonator, super-high-frequency band, thickness influence.

AIN/diamond heterostructures are very promising for high frequency surface acoustic wave (SAW) resonators. In their design, the thickness of the piezoelectric film is one of the key parameters. On the other hand, the film material quality and, hence, the device performance, also depend on that thickness. In this work, polished microcrystalline diamond substrates have been used to deposit AIN films by reactive sputtering, from 150 nm up to 3 um thick. A high degree of the c-axis orientation has been obtained in all cases. SAW one port resonators at high frequency have been fabricated on these films with a proper combination of the film thickness and transducer size.

Keywords: E-beam lithography Insulating layers Charge accumulation Anti-static layerThis work describes the electron-beam (e-beam) lithography process developed to manufacture nano interdigital transducers (IDTs) to be used in high frequency (GHz) surface acoustic wave (SAW) applications. The combination of electron-beam (e-beam) lithography and lift-off process is shown to be effective in fabricating well-defined IDT finger patterns with a line width below 100 nm with a good yield. Working with insulating piezoelectric substrates brings about e-beam deflection. It is also shown how a very thin organic anti-static layer works well in avoiding this charge accumulation during e-beam lithography on the resist layer. However, the use of this anti-static layer is not required with the insulating piezoelectric layer laying on a semiconducting substrate such as highly doped silicon. The effect of the e-beam dose on a number of different layers (of insulating, insulating on semiconducting, semiconducting, and conductive natures) is provided. Among other advantages, the use of reduced e-beam doses increases the manufacturing time.The principal aim of this work is to explain the interrelation among e-beam dose, substrate nature and IDT structure. An extensive study of the e-beam lithography of long IDT-fingers is provided, in a wide variety of electrode widths, electrode numbers and electrode pitches. It is worthy to highlight that this work shows the influence of the e-beam dose on five substrates of different conductive nature.

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