Jan H. Kuypers

Maximum accuracy evaluation scheme for wireless saw delay-line sensors

This paper describes an evaluation scheme that prevents phase ambiguity of surface acoustic wave (SAW) delay-line sensors. Although it is well-known that phase evaluation yields accuracies of 150~1500 times higher than time-delay evaluation, the problem of phase ambiguity has prevented phase evaluation of sensors operating over a range larger than 2 pi. This paper addresses this unsolved problem with a complete strategy. Furthermore, the existence of an optimum choice of the relative reflector positions on the sensor is shown. The presented relations enable the design of maximum accuracy SAW delay-line sensors.

P1I-9 Passive 2.45 GHz TDMA based Multi-Sensor Wireless Temperature Monitoring System: Results and Design Considerations

This paper presents a TDMA (time division multiple access) based wireless temperature monitoring system using 2.45 GHz passive surface acoustic wave (SAW) delay line sensors. A three-step resolution refinement scheme using a combined delay and phase evaluation is proposed. Using a transmission power of 2 dBm (1.59 mW) a temperature accuracy of 0.19 K and 0.1 K(6sigma), were achieved for an interrogation distance of 1.4 m, and 1.3 m, respectively. The sensor design is discussed using experimental results concerning the relationship between the SNR (signal to noise ratio) of the sensors and the accuracy in time delay or phase measurement. Also, the direct electron beam writing on chemically-reduced (black) LiNbO3 is described

P0-13 Phase Velocity Control of Surface Acoustic Waves Based on Surface Shorting and Electrical Field Application Using MEMS Switches

We have investigated controlling the phase velocity of a surface acoustic wave (SAW) by a microelectromechanical switch fabricated on a high coupling piezoelectric substrate. The principle is based on the interaction of the evanescent surface potential of the SAW with the conductive switch. In theory tuning of the velocity in the range given by v0 and vm, i.e. the velocity for a SAW on a free and metallized substrate, is possible. We have achieved up to 17.6 m/s (0.44 %) velocity tuning on 128degYX LiNbO3. A maximum velocity sensitivity of Deltav/v of 15times10-3/V and phase sensitivity of 700deg/V was measured. This is five orders of magnitude larger than values obtained for electrical field tuning.

MEMS based thin film 2 GHz resonator for CMOS integration

This paper describes the development of the aluminum nitride (AlN) thin film bulk acoustic resonator (FBAR) using noble MEMS techniques for CMOS integration. This resonator has an air gap between a substrate for acoustic isolation. Germanium (Ge) was used as a sacrificial layer to make the air gap. This technique gives simple process and high CMOS compatibility. The resonator achieved a Q factor of 780 and an effective electro-mechanical coupling constant (k/sub eff//sup 2/) of 5.36 % at a resonant frequency of 2 GHz.

2.45 GHz Passive Wireless Temperature Monitoring System Featuring Parallel Sensor Interrogation and Resolution Evaluation

We report on the development of a TDMA (time division multiple access) based wireless sensor system for temperature monitoring. The transponders consisting of passive surface acoustic wave delay line sensors were designed for operation in the ISM band at 2.45 GHz and for a temperature range from -20degC to 180degC. A multi-step evaluation scheme using a combined delay and phase analysis, is introduced. A temperature resolution of 0.19 K (6sigma) was achieved at a transmission power of +2 dBm (1.59 mW), when the distance between the transceiver and sensors was about 140 cm. We also report the importance of mounting the sensors during packaging based on experimental results.

Application of lithium niobate etch stop technology to SAW pressure sensors

This paper presents a process technology to form thin diaphragms with sealed cavities in a lithium niobate (LiNbO3) wafer, which will be used for small and sensitive SAW-based pressure sensors. The process technology uses thermal inversion, wet etching with an electroplated Au mask, etch stop at the thermal inversion layer and Au-Au bonding. By the combination of an etch stop and pinhole-free masking, LiNbO3 thin diaphragms with thicknesses of several tens of mum to 10 mum were fabricated in 128deg Y cut LiNbO3 wafers. The Au-Au bonding of the LiNbO3 wafer gave hermetic sealing. In addition the etch profiles of the LiNbO3 wafer predicted by Wulff-Jaccodine plots and observed in experiments were compared, and good agreement was confirmed.

Monolithic Phase Shifter Based on Mechanically Tunable Saw Delay Line

This paper presents results of mechanically controlling the phase velocity of surface acoustic waves (SAW) and the application to monolithic phase shifters operating at 0.1~10 GHz. A phase sensitivity of 2deg/V and sensitivity of the phase velocity (Deltav/v) of 41times10-6 /V have been measured for devices operating at 2.45 GHz. This is 2 orders of magnitude larger than existing SAW-based monolithic phase shifters. The acoustic wavelength being 10.000 times smaller than the free space equivalent together with the large sensitivity lead to a 50~500 times reduced device area compared to existing phase shifters.

Imprinted laminate wafer-level packaging for SAW ID-tags and SAW delay line sensors

We have developed a wafer-level packaging solution for surface acoustic wave devices using imprinted dry film resist (DFR). The packaging process involves the preparation of an imprinted dry film resist that is aligned and laminated to the device wafer and requires one additional lithography step to define the package outline. Two commercial dry film solutions, SU-8 and TMMF, have been evaluated. Compared with traditional ceramic packages, no detectable RF parasitics are introduced by this packaging process. At the same time, the miniature package dimensions allow for wafer-level probing. The packaging process has the great advantage that the cavity formation does not require any sacrificial layer and no liquids, and therefore prevents contamination or stiction of the packaged device. This non-hermetic packaging process is ideal for passive antenna modules using polymer technology for low-cost SAW identification (ID)-tags or lidding in low-temperature cofired ceramic (LTCC) antenna substrates for high-performance wireless sensors. This technique is also applicable to SAW filters and duplexers for module integration in cellular phones using flip-chip mounting and hermetic overcoating.

Aluminum nitride based thin film bulk acoustic resonator using germanium sacrificial layer etching

We report the development of aluminum nitride (AlN) thin film bulk acoustic resonator (FBAR). This resonator has an air gap beneath the resonator to obtain high Q factor and low spurious response. Germanium (Ge) was used as a sacrificial layer for the air gap. This technique gives very simple process and high CMOS compatibility. The FBAR was evaluated about the effect of the air gap and the electrode size. The FBAR achieved a resonant frequency of 2 GHz, a Q factor of 780 and an effective electro-mechanical coupling constant (k/sub eff//sup 2/) of 5.36%.

2.45 GHZ Saw-based passive binary transponder for wireless interfaces of integrated sensors

This paper describes the development of a MEMS tunable surface acoustic wave (SAW) device that allows an integrated sensor to be interrogated wirelessly in a range of several meters. The component itself requires no power for the wireless communication, as the principle is based on evaluating the reflected signal similar to a radar echo. The structure is similar to a one port reflective SAW delay line device. A MEMS switch is used to modulate the SAW according to the binary sensor output. The encoding solely requires an electrostatic tuning voltage of as low as 3 V for the MEMS switch. We successfully demonstrated that the device assembled on a microstrip antenna wirelessly transmitted ASCII characters over a distance of up to 2 m.