Quartz Crystal Units Research Articles

Precision Test Fixture for Measuring Equivalent Circuit Parameters of GHz Surface-Mounted Quarts Crystal Units

We developed a coaxial-type fixture for precisely measurement of the impedance characteristics of small surface-mounted quartz crystal units. This fixture is applicable to the one-port S-parameter reflection method proposed in IEC60444-5, and measures the frequency impedance characteristics of a device under test (DUT) from its reflection coefficients. This measurement fixture uses a 65 GHz coaxial connector and calibrators with a 1.85 mm inside diameter. Using a “zero-length” coaxial center pin method, this fixture can be applied to up to 2 GHz devices without the need for electrical length compensation.

The frequency adjustment method of quartz crystal unit using a quick response evaporation source

AbstractIn the manufacture of quartz crystal units, there is a frequency adjustment process in which the individual frequencies are measured and matched to each other, resulting in a frequency adjustment method based on the use of a resistance heating evaporation source to deposit Ag, Au, and other electrode materials. The frequency measurement method used for quartz crystal units has been the oscillation method, and we proposed a transmission method based on a network analyzer and π circuit to improve measurement precision, and a standby method based on a CW sweep to increase measurement speed. We then developed a quick response evaporation source control method adapted for the proposed method. Because the CW sweep standby method sweeps only one point, measurement can be performed in a shorter time than with a linear sweep. In addition, since we were able to perform high‐precision adjustment in a short time, we implemented rate switching, starting adjustment at a high rate and finishing at a low rate, and then controlled the evaporation source so that the rate remained fixed during standby time. As a result, we were able to switch the rate in three stages for a normal frequency adjustment volume of about 1000 ppm, achieving adjustment of ±2 ppm during the deposition time of 2.5 seconds. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(1): 11–19, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20282

Evaluation and evaporation to exact resonance frequency (32.768 kHz) of semifinished and unsealed surface mount device (SMD) quartz tuning fork resonators

Evaporation to exact resonance frequency was manually carried out one at a time on the semifinished and unsealed surface mount device quartz tuning fork crystal units fabricated by employing positive (subtractive) photolithography, selective etching and subsequent positive (subtractive) photoresist spray coating method. Finite element method was used as a theoretical modeling tool to correlate mass of further metal to be deposited onto the tips of the tuning fork tines and decrease of resonance frequency. It was also necessary to evaluate as-fabricated tuning fork crystals prior to final frequency adjustment plating process and they were tested in both air and vacuum-sealed environments to obtain various crystal parameters, most importantly variation of quality factor or Q-value with pressure. Subsequent to evaluation, tuning fork resonators were successfully fine-tuned to exact resonance frequency by 32.768 kHz + 5.7 ppm proving that evaporation to exact resonance frequency method is equally effective compared with trimming method by laser beam, etc.

The Resonating Properties of a Crystal Unit of Fundamental Frequency 150 MHz

150 MHz rectangular AT-cut quartz crystal units were prepared by means of photolithography. For the elimination of the effect on a frequency response by the mechanically damaged layer, chemical etching on both sides was employed. Gold evaporated films were used as the electrodes for frequency stability during long-term driving. As a result, crystal units which had excellent frequency stability during long-term driving and low crystal impedance were obtained. Furthermore, a Colpitts crystal oscillator was constructed, and some experimental data are presented.

Synthetic Quartz Production and Applications

The process of hydrothermally growing single crystals of quartz in high pressure autoclaves at elevated temperatures is described in brief. Methods of cutting and processing of wafers of quartz from synthetically grown crystals for fabrication of quartz crystal resonator units are outlined. The principle of operation of quartz crystal units is explained with the aid of an equivalent LCR circuit and the method of controlling precisely the frequency of oscillator circuits by a quartz resonator is elucidated. Extensive applications of quartz in the emerging electronic era are reviewed, both for analogue and digital circuitry, and the Indian demand analysed in the perspective of production capacity of a leading developed country of the world.

Determination of parameters of VHF quartz crystal units equipped with evaporated electrodes using an Fr‐meter fixture

AbstractThe Fr meter method is described as a method of measuring quartz crystal units in Appendix 1 of the Japanese Industrial Stand ard (JIS). When the resonance frequency and equivalent parameters of a quartz crystal unit are measured with the Fr‐meter fixture, an equivalent circuit based on four parameters has usually been employed. However, this equivalent circuit is not accurate for representing the impedance characteristic of the unit over a wide frequency range. to solve this problem, this paper offers an accurate method based on an equivalent circuit having five parameters for measuring the parameters over a wide range (from fs to fp) with the Fr meter fixture. the method is based on an equivalent circuit having five parameters.This paper describes the principle of the method; measurements of VHF‐band quartz crystal units; comparisons of the results with those obtained by using the drop method; and an examination of the repeatability of the method. the results show that the standard deviation of the resonance frequencies is within 2 × 10‐8, and the frequency agrees well with that obtained by the drop method. the characteristics between frequency and impedance of quartz crystal units calculated by using the parameters obtained agree well with those measured. It was confirmed that the proposed method with the Fr‐meter fixture could accurately measure the resonance frequency and the parameters of quartz crystal units.

Quartz Crystal Units for Temperature Compensated Crystal Oscillators

Quartz crystal units in the frequency range of 2.48 MHz to 5.0 MHz were designed and fabricated for use in Temperature Compensated Crystal Oscillators (TCXO's). Their dynamic and static behaviour of frequency and resistance with respect to temperature changes from–45°C to +85°C were studied. The geometry of the resonator namely, the resonator diameter, piano convex contour, electrode thickness and size were properly selected to make them free from activity dips and frequency discontinuities in the desired temperature range. The resonator quality factor [Q] was estimated with different amount of etching in NH4 HF2 solution and an optimum level of etch was determined. Quality factors around 0.6 million could easily be achieved at 3.5 MHz in all the production batches. Crystals processed and encapsulated in HC-6/U cold weld enclosure with < 10−6Tor vacuum showed an ageing rate of few parts in 10−7 per month. At 3.2 MHz and 3.5 MHz several thousands of these crystal units were successfully manufactured in the...

An Investigation of Aging in a Quartz Crystal by VLF Phase Comparison Method

Abstmcf-The objective of the study presented here is the determination of aging characteristics of the local crystal which has been in continuous operation for fifteen years. To do this, the data accumulated since 1968, by phase comparison of the local crystal with the 16 kHz primary standard frequency emitted from Rugby, England, has been analyzed from the point of view of aging in the local crystal. The aging rate, which was parts in lo9 per day at the very early phase of operation of the local crystal, came down to parts in 10l2 per day at present. In this study an AT-cut rectangular quartz plate vibrating at 5 MHz is used. Since there is not a unique theory of aging in literature for crystal resonators, an attempt to explain the time dependence of the aging rate for the AT-cut crystal chips is made by making use of observed aging characteristics. It is believed that the study may help in the developments of nonaging quartz crystal units.

Long-term frequency variations of quartz crystal units under different environmental conditions

The present article describes the results of investigation of frequency ageing of several the most widely used quartz crystal unit types (designs). These investigations were carried out both under operating and non operating conditions and under different temperatures. It is shown that the 10°C variation only of the ambient temperature increases the frequency ageing by 1.5-2 times. The influence of the drive level and some other factors on the frequency ageing is also mentioned in the article.

Appraisal of the inverted-mesa AT-cut quartz resonator for achieving low-inductance high- Q single-response crystal units

A novel design for v.h.f. AT-cut quartz-crystal units is described which enables optimum energy-trapping conditions to be achieved with less restriction in the choice of equivalent electrical parameters than is usual for conventional units. The good suppression of unwanted modes, low inductance values and potentially good frequency stability of this type of unit should lead to its application in both oscillators and filters.

Quartz crystal unit measurement method based on transmission line T-network

A method for the investigation of quartz crystal units by phase technique with application of a special T·network is presented. The construction of the T-network using microwave techniques, is proposed. The transmission line T-network enables an accurate measurement of basic parameters of crystal units-resonance frequency (F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) and resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) to be made in a wide frequency range. As opposed to the well-known π-network, this T-network allows unique, more precise determination of its parameters and, in consequence, achievement of higher measurement accuracies. Results of an investigation of this T-network, T-513 model, show actually attainable accuracies of measurements ΔF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> /F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> < ±10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> , ΔR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> /R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> < ±4% in the frequency range 1-100 MHz. By means of the presented T-network, a direct measurement of the series resonance frequency (F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ) is possible, too. Knowledge of the T-network parameters renders determination of the measurement accuracy possible also if a different technique than the phase one is used, e.g., FM technique. The method using the transmission line T-network was proposed for acceptation to IEC as a basic method for the measurement of quartz crystal units by phase technique.

Morphological Features Associated with Polished Quartz Surfaces

The ability of quartz crystal units to perform as highly precise single sideband resonators for frequency control is marred by their long-term aging characteristics. After a stabilization period of four weeks, during which time crystals are maintained at their upper turning point temperature, a long-term aging rate of &lt;±2xl0-10 /week frequency deviation is desired. Various explanations of this frequency drift greater than this value have been proposed (1,2). One of the most prevalent theories of quartz aging is that it results from ·minute changes that occur over a period of time in the chemical and physical nature of the resonator surface. In a carefully designed program to construct very low-aging quartz resonators, we included electron optical surface characterization techniques.

Low aging quartz crystal units

A new process is described whereby quartz crystal units are vacuum baked, plated, and sealed during one and the same pump-down cycle. The crystal blanks are mounted by means of gold rivets and plated with copper. The performance potential of the resulting "clean" and "strain-free" crystal units is demonstrated at 62 MHz where aging rates below ±5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> per week and Q values of 200 000 are obtained.

Effect of High-Temperature Processing on the Aging Behavior of Precision 5-MHz Quartz Crystal Units

The influence of contamination level on the aging behavior of quartz crystal resonators has been studied. Resonators were made using high-temperature bonding techniques and were baked prior to sealing in both dry hydrogen and under high vacuum in order to minimize the level of contamination within the enclosure. The initial stabilization period for the frequency drift rate to reach 3 parts per 1010/month and the period to restabilize after power interruption to oven and oscillator is usually less than a week for these units. The time periods to reach the same drift rate for units made using the current state-of-the-art fabrication tecnhiques range from one to six months. The difference in aging behavior is discussed in terms of a possible aging mechanism.

Increased resistance of crystal units at oscillator noise levels

Problems have been experienced with inoperative military equipment which have been traced to a defect in some quartz crystal units. This defect has been determined to be an increase in resistance (loss of Q) of crystal resonators when excited at very low power levels. The typical crystal oscillator, when first turned on, excites the resonator with thermal noise and consequently the power dissipated is very small. Simple instrumentation has been assembled to show clearly the low power increased crystal resistance effect. Tests have shown that surface defects, due to the final lapping process, contribute to the problem. The necessity of surface etch to remove the damaged surface layer is shown to be required to avoid defective crystal units.

State of the art—Quartz crystal units and oscillators

The paper discusses progress made in the field of quartz crystal units and quartz crystal controlled oscillators over the past few years. The field is reviewed in general, but several accomplishments which are thought to be of special importance, are discussed in detail. These subjects include, among others, quartz vibrator characteristics and enclosures, modes of motion including the trapped energy concept and long-term drift (aging) of crystal units. The characteristics of various types of oscillators are reviewed including temperature compensated and high precision types, and the problem of short-term stability of crystal controlled oscillators is discussed. Precision oscillators are available today with a daily drift rate as low as a few parts in 1011and a short time stability better than a few parts in 1010for a time period of one millisecond.

Unwanted responses in VHF quartz crystal units

Unwanted responses in VHF quartz crystal units

Design and performance of thickness-shear vibrating quartz filter crystals

A study has been made of the effect of crystal-blank and electrode geometries on the performance of AT-cut and BT-cut quartz-crystal units intended for use in filters. Methods for controlling the frequencies and activities of unwanted modes of vibration are described, and it is shown that, by scaling the geometries, it is possible to translate crystal designs from one frequency to another. At frequencies below about 10 Mc/s, the unwanted spectrum of inharmonic thickness-shear resonances can be modified by the application of acoustically lossy material and the vacuum deposition of metal layers on to regions of the crystal which are most active for these modes of vibration. Above 10 Mc/s, it is found that the motional area of the crystal does not extend far outside the central electroded area, and, in view of this, it is possible to have more than one resonant section on the miniaturisation. Frequency/temperature between thickness-shear vibrations and influenced by the electrode thickness and same quartz blank, thereby obtaining a considerable degree of and activity/temperature characteristics, illustrating coupling high overtones of low-frequency resonances, are shown to be the method of mounting the crystal.

Piezoelectric Effect and Applications in Electrical Communication

The phenomenon of piezoelectricity, discovered in 1880, is the basis of a number of devices which are essential to the art and practice of electrical communication. The discovery of the phenomenon, the development of the quartz resonator, and its application as a frequency-stabilizing element in oscillator and filter circuits are described. Some of the technical problems encountered in the design and fabrication of quartz-crystal units are discussed. Using quartz crystal units for short-term stability and atomic resonators for long-term stability, frequency standards which are reliable and reproducible to 1×10-11 are now available.

Design and Performance of Ultraprecise 2.5-mc Quartz Crystal Units

A 2.5-mc crystal unit has been developed for use in a new, extremely stable frequency standard oscillator. A well-balanced design was achieved by using a 30-mm-diameter, plano-convex, polished quartz plate, coated with gold and operated on its fifth overtone. The quartz plate is mounted on its quiescent edge in an evacuated bulb, and achieves a Q of five to six million, representative of the Q of the quartz itself. The temperature coefficient, current coefficient, frequency adjustment tolerance and frequency aging of the crystal unit are all consistent with a frequency stability in the order of one part in 1010. It was necessary to develop polishing methods that would not disturb the crystal structure of the quartz plate and new methods of orienting the crystollographic axes to achieve better temperature coefficient control. New methods of mounting the quartz plate were found that avoid strain and reduce the effects of shock and vibration. The new crystal unit makes possible oscillators characterized by excellent frequency stability, small and uniform aging and straightforward design. For periods up to one month, the frequency stability of such standards compares favorably with that of atomic frequency standards.