Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-08-31
2002-09-10
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06448699
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to oscillators that provide a stable reference source or frequency in computers or other electronic equipment. Specifically, there is an electrode configuration for a crystal resonating device that provides less mode coupling and improved spurious noise suppression.
2. Description of the Prior Art
Various devices are well known for providing a reference frequency or source. Such devices are called oscillators. The oscillator typically has a quartz crystal source and also has electronic compensation circuitry to stabilize the output frequency. Ovenized oscillators heat the oscillator to a uniform temperature to obtain a more stable output frequency. The oscillators have been packaged on various support structures and in housings such as metal cans.
The quartz crystals have electrodes patterned on each side of the crystal. The electrodes are used to apply a voltage across the crystal. The electrodes are typically made by vacuum thin film depositing a metal such as gold through a mask onto the surface of the crystal. A typical prior art electrode configuration
10
is shown in
FIG. 1. A
conventional quartz crystal blank
12
has a top surface
1
2
A and a bottom surface
12
B. A top electrode
14
is located on top surface
12
A and a bottom electrode
20
is located on bottom surface
12
B. Top electrode
14
has a contact portion
16
and a circular central portion
18
. Similarly, bottom electrode
20
has a contact portion
22
and a circular central portion
24
. The contact portion would be attached to another electrical contact such as a substrate pad or a crystal clip in order to make an electrical connection to another electrical circuit such as an oscillator whose frequency is desired to be stabilized. The area where electrodes
14
and
20
are directly overlapping each other is indicated by area
26
. As the crystal frequency is increased, the required area of the electrodes decreases. In the range of 155 Mhz, the typical electrode would be approximately 0.024 inches in diameter.
The ever increasing demand on the crystal industry today is for devices with reduced size. Due to the reduced diameter to thickness ratio in miniature quartz resonators that typically operate in thickness shear mode, coupling to unwanted flexural, face shear and thickness twist modes is very difficult to avoid. When one of these modes is excited, considerable energy transfer from the main mode to the undesirable coupled mode can occur. This results in an increase in the resonators motional resistance and will also cause a change in the frequency of resonance at a given temperature. This can cause a failure of the oscillator built with such a resonator. The oscillator may stop oscillating if the gain of the oscillator is not sufficient to compensate for the increase in the resonators series resistance. The oscillator may also fail the frequency stability requirement. For the preceding reasons, screening of finished resonators for coupled modes is usually done before they are installed in an oscillator. Typically, 1 to 10 percent of the tested resonators are defective depending on the resonator design and oscillator specifications.
Several resonator design parameters effect coupling to undesired modes. Some of these are resonator dimensions, resonator contour diopter, edge bevel, electrode size and the amount of plate-back. Frequently, many of these parameters cannot be varied because of resonator electrical parameter requirements. The main cause of bandbreaks in quartz crystals with circular geometry is coupling via non-linear elastic properties to one particular type of mode excited at integral multiples of flexure and face shear modes. Bandbreak clear regions are to expected when the electrodes span a whole number of wavelengths and terminate at nodes. Circular electrodes are clearly incompatible with this criterion for the suppression of coupling.
A current unmet need exists for an electrode design for a crystal that suppresses mode coupling.
SUMMARY OF THE INVENTION
It is a feature of the invention to provide a crystal electrode that suppresses unwanted mode coupling.
Yet, another feature of the invention is to provide an electrode for a crystal that includes a crystal blank that has a top surface and a bottom surface. A first electrode is located on the top surface. The first electrode has a contact portion and a polygonal portion. A second electrode is located on the bottom surface. The second electrode has a contact portion and a polygonal portion. The polygonal portions of the first and second electrodes are arranged such that they oppose each other.
REFERENCES:
patent: 2994791 (1961-08-01), Shinada et al.
patent: 4123680 (1978-10-01), Kemper et al.
patent: 6133673 (2000-10-01), Kawara et al.
patent: 6346762 (2002-02-01), Watanabe et al.
patent: 45-20226 (1970-09-01), None
Miernicki Leon J.
Scepanovic Dragan
Borgman Mark W.
Bourgeois Mark P.
Budd Mark O.
CTS Corporation
LandOfFree
Octagonal electrode for crystals does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Octagonal electrode for crystals, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Octagonal electrode for crystals will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2890228