The radio-frequency identification (RFID) concept is expanded to millimeter-wave frequencies and millimeter-wave identification (MMID) in this paper. The MMID concept and a comparison with UHF RFID are presented, showing the limitations and benefits of MMID. Three feasible applications are suggested for MMID, which are: (1) wireless mass memory; (2) an automatic identification system with pointing functionality; and (3) transponder communication with automotive radar. To demonstrate the feasibility of the MMID system, experimental results for both downlink and backscattering-based uplink are presented at 60 GHz.

This letter investigates the applicability of Sezawa propagation mode for various GaN/Si surface acoustic wave (SAW) temperature sensor structures. First, different acoustic propagation modes in GaN on Si single SAW resonators, operating at GHz frequencies, were evaluated. The variation of the phase velocity versus the normalized thickness of the GaN layer is analyzed experimentally for different propagation modes, on the SAW structures manufactured using e-beam lithography. The different acoustic modes were also identified using finite-element method calculations. The effective coupling coefficients for the Sezawa mode are determined and show larger values than those obtained for the Rayleigh mode. The sensitivities obtained for the temperature sensor structures are 1.8 times higher for Sezawa than for the fundamental Rayleigh mode.

This letter describes the fabrication and the morphological and microwave characterization of film bulk acoustic resonator structures, supported on very thin GaN membranes. We have demonstrated, by employing both white-light profilometry as well as X-ray diffraction, the low deflection and low stress of the GaN membranes supporting the resonator metallization. Using as test structure two FBAR structures connected in series, by a floating backside metallization, we have obtained resonance frequencies of 6.3 GHz for a 0.5-mum-thick membrane. The quality factor, at 6.3 GHz, was higher than 1100.

This paper presents the fabrication and characterization of a GHz operating SAW based pressure sensor on a 1.2 μm thin GaN membrane. Two types of interdigitated transducers are manufactured using electron beam nanolithography to obtain finger and interdigit spacing widths - one with 170 nm and the other 200 nm half pitch. Micromachining techniques are used to obtain the 1.2 μm thin membrane. The resonance frequency shift of the SAW, the pressure sensitivity, sp, as well as the pressure coefficient of frequency, PCF, were experimentally determined and analyzed, both for the Rayleigh as well as for the symmetrical Lamb propagation mode, in the 1 to 7 Bar pressure range. Record values for sp (up to 6 MHz/Bar) and PCF (up to 537 ppm/Bar) have been obtained, especially for the symmetrical Lamb propagation mode also due to the very high frequency operation (5-11.5 GHz). The effect of different orientations of the SAW device (in the [1100] and [1120] directions) on the frequency response and sensitivity is also analyzed. The possibility to determine simultaneously the pressure and the temperature with the same SAW structure operating as a dual sensor has been demonstrated.