A comparison is given between piezoelectrically excited bulk acoustic wave (BAW) and surface acoustic wave (SAW) elements with respect to their primary sensitivity functions and principal capabilities for sensor applications. The importance of mode purity for high dynamic range sensors is emphasized. Characteristic sensor examples are reviewed, and the special demands on the electronics for BAW and SAW elements in the sensor field are described (e.g., cable problem, wireless SAW sensors). For a fair evaluation, a performance figure, SQ, defined as the product of reduced sensitivity S and resonator Q-value, is introduced. The potential of alternative piezoelectric materials for future sensor developments is discussed briefly.

Comparison between BAW and SAW sensor principles

This work reviews the use of thickness shear mode resonators for temperature sensing and pressure measurement. Advantages of such sensors include inherently digital format, high resolution, high accuracy, and long-term stability. This work reviews the physical principles involved in the operation of the devices along with quoted sensor performance results. The earliest commercially available temperature sensors were stand-alone units. Their use and commercial success evolved through different stages depending in part on ancillary electronics available at the time. A number of temperature-sensing applications are ancillary to other thickness shear resonator sensors. Two main categories are separate resonator for temperature compensation and dual-mode operation of a single thickness shear resonator. Dual-mode oper- ation subdivides into use of two modes from different thickness shear mode families or two modes from the same thickness shear mode family. A variety of pressure sensors use the fact that the frequency of a thickness shear resonator changes with stress bias. Such applica- tions divide conveniently into categories dependent on the pattern of stress bias used.

Review of thickness-shear mode quartz resonator sensors for temperature and pressure

Disclosed is an oscillator that relies on redundancy of similar resonators integrated on chip in order to fulfill the requirement of one single quartz resonator. The immediate benefit of that approach compared to quartz technology is the monolithic integration of the reference signal function, implying smaller devices as well as cost and power savings.

Temperature compensated oscillator including MEMS resonator for frequency control

Dual mode excitation of resonators allows the highly accurate measurement of, and compensation for, the effects of temperature, pressure, etc., by means of frequency measurements alone. Frequency can be measured with far higher accuracy than any other quantity. In dual mode excitation, the two excited modes occupy the same volume of quartz, thereby allowing the resonator to sense two measurands simultaneously, e.g., pressure and temperature. This paper reviews the dual-mode technique and its sensor applications.

Temperature-insensitive dual-mode resonant sensors - a review

Frequency can be measured with far higher accuracy than any other quantity. Dual mode excitation of resonators allows the highly accurate measurement of, and compensation for, the effects of temperature, pressure, etc., by means of frequency measurements alone. In dual mode excitation, the two excited modes occupy the same volume of quartz, thereby eliminating gradients between the resonator and sensor. This paper reviews the dual-mode technique and its applications in oscillators, clocks and sensors.

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Dual-mode oscillators for clocks and sensors

There is very attractive idea to use SC-cut resonators excited on B and C modes for frequency stabilization (in particular, for digital thermocompensation) but up to now these operating regimes are used very seldom. The cause consists in a difficulty to get stable excitation in wide temperature range. Due to development of original resonator excitation networks, of special geometry of piezoelement and due to original technology of its manufacture, we succeeded in developing of B and C modes in wide (-60...+85)/spl deg/C temperature range. 70% yield of suitable units is attainable when resonators are exited on 10 MHz frequency using 1st mechanical harmonic. The requirements to a circuit of a dual-mode oscillator (that is oscillator capable of simultaneous exiting on two asynchronous frequencies) are presented. A lot of experiments have been involved to design double-mode crystal meeting the requirements assigned above. To avoid the dips of activity of the B-mode being inherent property of overton SC-cut crystals due to nonlinear interaction of the thickness modes the fundamental mode TD-cut (yxb1/23/spl deg/25'/34/spl deg/) crystal plate has been used here. Exploration of the modes activity behavior over a wide temperature range has shown that the motional resistance remains within (8-12) Ohms for C-mode and (50-65) Ohms for B-mode. Practical realization of the dual-modes oscillator in the form of a hybrid LCI is described. The dual-mode crystal oscillator parameters are: output frequency 10 MHz; supply voltage 5V; consumption current 5-7 mA; output levels TTL. >

A.V. Kosykh

Papers

Dual-mode crystal oscillators with resonators excited on B and C modes