Piezoelectric resonators are well known in the art. Piezoelectric resonators are electronic elements used to select and make a frequency stable. Piezoelectric resonators are widely used in various kinds of electronic equipment including communication systems, intelligence sensors, precision guided munitions, cordless telephones, broadcast and television, satellite telecommunication, electronic clocks, digital instruments and so on. Piezoelectric resonators can also be used as sensors of temperature, pressure and weight. One of the shortcomings and limitations with piezoelectric resonators is that they are prone to undesired shifts in resonance frequency when they experience external acceleration or vibration.
The advent of modern personal satellite communications systems has transformed acceleration sensitivity from a military-specific technology barrier to an important concern for commercial systems. The vast majority of communications systems maintain phase coherence by using low-noise oscillators. Commercial off-the-shelf crystal oscillators are capable of meeting nearly all systems requirements, provided that the systems are at rest.
The problem of acceleration sensitivity has been the subject of research for more than 30 years, initially at Bell Labs and Hewlett-Packard, and later at the U.S. Army Electronics Technology and Devices Laboratory and the U.S. Army Research Laboratory. Additional efforts have also been pursued by the U.S. Army Research Office and the French Laboratorie de Chronometrie et Piezoelectric. Yet none of these efforts has succeeded in providing a clear and complete understanding of the fundamental nature of acceleration sensitivity in piezoelectric resonators. As a consequence, previous approaches to reduce acceleration sensitivity that are based on an imperfect understanding of the acceleration phenomenon have been less successful than desired. Such unsuccessful efforts include ring-supported resonators, aspect-ratio compensation, visco-elastic mounting and mode shape modification. Each approach offers a particular set of advantages, but they all suffer from the common disadvantage of excessive acceleration sensitivity. None of these unsuccessful techniques has yet to yield a piezoelectric resonator with acceleration insensitivities repeatedly below 1×10−10/g.
The stresses caused by acceleration, vibration and shock are well known to those skilled in the art. Periodic acceleration in the form of vibration can cause frequency modulation in piezoelectric resonators, and shock can cause a step frequency change in a piezoelectric resonator due to the typical piezoelectric resonator's acceleration sensitivity. Shock can also cause a permanent frequency change in a piezoelectric resonator if either the supporting structure or the electrodes is stressed beyond their elastic limits. Therefore the stresses caused by acceleration, vibration and shock and the consequent significant effects on piezoelectric frequency instability have caused prior art piezoelectric resonators to suffer from numerous disadvantages, limitations and shortcomings. Current piezoelectric resonators continue to suffer from the long-standing difficulties, shortcoming and limitations associated with excessive acceleration sensitivity and do not provide acceleration insensitivity repeatedly below 1×10−10/g. Up until now, there has been a long-standing and continuing need for piezoelectric resonators with repeatable acceleration insensitivities on the order of below 1×10−10/g. Thus, there has been a long-felt need to provide piezoelectric structures that reduce the undesirable and harmful effects of the stresses caused by acceleration, vibration and shock and provide affordable and easy to produce piezoelectric resonators.
The structures of the present invention provide added support and restraint techniques that significantly reduce the undesirable effects of acceleration sensitivity through a plano—plano piezo-microresonator, a plurality of gaps and a rigid structural securing member that can essentially eliminate any excessive sensitivity, without suffering from the long-standing disadvantages, limitations and shortcomings of prior art acceleration sensitive resonators. The piezo-microresonators of the present invention satisfy the long-standing and continuing need for piezoelectric resonators with repeatable acceleration insensitivities on the order of less than 1×10−10/g with an acceleration insensitive plano—plano piezoelectric resonator with a predetermined proportionality constant that is supported by a rigid support member, without suffering from the disadvantages, shortcomings and limitations of prior art resonators.