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High Stability Crystals
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The stability characteristics of a crystal resonator over temperature and time are key components in the design of precision oscillators for wireless base stations, precision test and measurement equipment, network timing sources and military communications equipment. Vectron's crystal resonators are designed and manufactured to achieve the best possible stability performance. Design and simulation tools have been developed to achieve resonators with consistent performance over temperature, delivering outstanding results for precision TCXO's and OCXO's. Custom developed equipment and processes are optimized to deliver exceptional aging performance.

Aging Performance

One of the main causes of crystal aging is mass transfer to or from the resonator surfaces (due to adsorption and desorption of contamination). Contamination of a single monolayers adsorbed or desorbed from the quartz surfaces has a resulting frequency change on the order of parts per million. Therefore, in order to achieve low–aging, crystal units must be fabricated and hermetically sealed in ultra–clean, ultra–high vacuum environments.¹

Sealing Technology:
Vectron has developed Ultra High Vacuum (UHV) cold welding equipment to achieve the ultra-clean environments required for low aging (pictured at right). Parts loaded into bake-out chamber and baked at high vacuum (10-9 Torr) and high temperature to allow complete outgassing of the surfaces. Parts are then manipulated to a cold weld die where the package and lid are fused together with 20 tons of force.

Ultra High Vacuum cold welding technology photo

Results achieved with the UHV welder are exceptional as shown with the example at right for a 5MHz 3rd OT SC–Cut resonator.

The projection for the 5MHz 3rd OT SC Cut resonator aging plot at right is less than 5ppb at 20 yeaars

Displacement & Rates plot

Resonator Design & Activity Dip Performance

All crystal resonators have a 3rd order function with Temperature. Anomalies in the F vs. T and R vs. T characteristics, as illustrated at right, are called "activity dips" and affect both the frequency and the resistance of the resonators.

Activity dips are usually caused by interfering modes of vibration, typically high overtone flexure modes. When the frequency of the interfering mode coincides with the frequency of the main mode, energy is lost from the main mode and an activity dip occurs.¹

Activity Dip Performance Plot image

The job of the crystal designer is therefore to find a design where the primary mode of resonance is not interfered with by any of the other modes present in the resonator over the Temperature range of interest.

Vectron has developed design and finite element analysis simulation tools that allow us to anticipate and avoid interference from unwanted modes delivering activity dip free performance.

The graphic at right is a simulation of the desired C–mode resonance of an SC–Cut resonator. The graphics below show various overtone and flexure modes.

Simulation of the desired C-Mode resonance image

Modes of Vibration in a 10MHz SC–Cut Crystal Resonator
SC10 311 Mode:
SC10 311 Mode displacement image

SC10 115 Mode:
SC10 115 Mode displacement image

SC10 133 Mode:
SC10 133 Mode displacement image
SC10 113 Mode:
SC10 113 Mode displacement image

SC10 131 Mode:
SC10 131 Mode displacement image

SC10 151 Mode:
SC10 151 Mode displacement image

John Vig Tutorial
[1] J.R. Vig, "Quartz Crystal Resonators and Oscillators – For Frequency Control and Timing Applications – A Tutorial", January 2004

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