GT-cut quartz crystals are smaller, more stable for lower-MHz frequencies
The company has specialised in 10-MHz range GT-cut components and precision photolithography. Originally developed in the 1940s as components offering outstanding frequency-temperature characteristics, GT-cut quartz crystal units have posed challenges in blank fabrication, limiting volume production. AT-cut quartz crystals have seen a shift toward support for higher frequencies to respond to a trend of smaller packages, creating a need for smaller, low-power units operating at lower MHz frequencies.
GT-cut quartz crystal units can provide;
– Compact, low-profile unit operating at lower MHz frequencies – the width-extensional mode of GT-cut quartz crystal units (Fig. 1) allows package design unconstrained by blank size, in turn enabling significantly smaller and lower-profile units operating at lower MHz frequencies, characteristics difficult to achieve with traditional AT-cut quartz crystal units. (See Table 1.) The equivalent circuit constants of GT-cut quartz crystal units are comparable to those of AT-cut units.
– Stable frequency over a broad range of temperatures – GT-cut quartz crystal units are known for their frequency-temperature characteristics (Fig. 2). This development yields units with an outstanding value of ±3 ppm in the range of −20 to +70°C and/or ±5ppm in the range of −40 to +85°C: performance not possible with AT-cut quartz crystal units.
– Can be driven at low power – with the acknowledged difficulty of achieving stable low-power vibration with AT-cut quartz crystal units, they are typically driven at 10 μW or more. In contrast, GT-cut quartz crystal units permit the design of oscillators that minimise vibration loss and ensure stable oscillation, even when driven at 5 μW or less.
Battery-powered mobile devices are often designed to operate intermittently to help minimise power. Compared to traditional compact AT-cut quartz crystal units, GT-cut units achieve starting oscillation time approximately twice as fast—in 550 μsec (compared to 12 MHz FCX-05 in the same oscillation circuit and at the same frequency).
River Eltec has experience of developing products that harness contour-mode vibration, including Lame-mode resonators, leading to technical and design expertise for various vibration modes, and the GT-cut quartz crystal units capitalize on this knowledge. These units use a contour-mode vibration in their width-extension mode.
GT-cut quartz crystals are produced using precision fabrication in an order of several microns (μm),
applying precision photolithography techniques refined through the production of tuning fork quartz
crystal units. They employ e-beam sealing for reliability; air-sealed with metal lids welded onto a ceramic package using a proprietary ebeam sealing technique. This protective seal guarantees high core performance by maintaining a high vacuum condition inside the package.
Other specification points include parallel capacitance of 5.0 pF max, insulation resistance 500 MΩ min. at 100V DC ±15V; level of drive 10 μW max; motional resistance (ESR) 400 Ω max. (12 MHz).
River Eletec; www.river-ele.co.jp
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