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KYOCERA Reduces Resistance during Oscillation by 25% to 60Ω in New Small-Sized CX1612SB AT-Cut Crystal Unit for Wireless Communications

Application of photolithographic processing improves CI value and cuts lead-time for design prototypes by more than half

January 10, 2012

Kyocera Corporation (President: Tetsuo Kuba) and its wholly-owned subsidiary in charge of quartz crystal device development and manufacturing, Kyocera Kinseki Corporation (herein “Kyocera Kinseki”), announced the successful development of the new CX1612SB AT-Cut Crystal Unit which was achieved through application of a photolithographic process. The new product achieves a crystal impedance (CI) value (motional series resistance) of 60Ω, a 25% improvement over conventional products.

Kyocera Kinseki will provide samples of this product starting in March 2012, and start mass production with a target of 500,000 units per month starting in the summer of 2012. The product will be sold by regional Kyocera Group companies.


Name

CX1612SB Crystal Unit

Application

Reference signal oscillation for wireless communication handsets

Dimensions

1.6 x 1.2 x 0.3mm

Production facility

Kyocera Kinseki Yamagata Corporation, Kyocera Kinseki Corporation / Shiga Yohkaichi Plant

Sample availability

From March 2012

Frequency stability

±15 × 10-6/+25℃ ±3℃

Frequency temperature stability

±15 × 10-6/-10 to +70℃
(deviation from the frequency at 25°C)

CI value
(motional series resistance)

60Ω max. (38.4MHz fundamental wave, reference value)

Photo:CX1612SB 1612 size AT-cut crystal unit
CX1612SB 1612 size AT-cut crystal unit
(1mm increments shown)

The AT-cut crystal unit, a component that oscillates the reference signal for ICs, is widely used in various electronic devices such as mobile phones, smartphones, and healthcare devices. In recent years, higher precision has been required of the oscillator units due to the increasing functionality of these devices. However, there are limitations on the processing accuracy in the conventional machine lapping process*1, resulting in variations in characteristics as well as design prototypes requiring a period of two to three months to complete.

By developing a unique manufacturing technology to apply photolithographic processing, which allows numerous minute patterns to be formed on one crystal substrate (wafer), Kyocera Kinseki has solved these problems and succeeded in developing a product that improves the CI value by 25% and cuts lead-time for design prototypes by more than half.

1. CI value reduced to 60Ω, a 25% improvement over conventional products
By achieving control of dimensional variations and processing strain on the crystal element, as well as forming a crystal element in a unique elliptical and convex (mesa*2) shape by utilizing advanced design technology, the CI value has been reduced to 60Ω, a 25% improvement over the 80Ω of machine lapping processed products.

2. Period for design prototypes shortened to a minimum of one month
In the machined lapping process, it takes two to three months to divide and lap crystal elements. However, with photolithographic processing the lapping process is unnecessary and numerous elements can be simultaneously formed on one crystal wafer. This shortens the lead-time for design prototypes to a minimum of one month, less than half the previously required time.

By utilizing these manufacturing technologies established through the photolithographic processing of the AT-cut crystal unit, Kyocera Kinseki will aggressively engage in the development of high-precision components and strive for further product miniaturization.


Advanced Element Technology Possessed by Kyocera Kinseki
The newly developed product was realized by combining the application of photolithographic processing with the following technologies which have been amassed over the years by Kyocera Kinseki.

1. High-quality synthetic crystal growth technology
Superior technology for synthetic crystal growth (autoclave conditions, materials, cleaning, etc.) which have been accumulated in over 50 years of experience by Kyocera Kinseki and a growth autoclave with a diameter of 650mm — allowing for production of large-size synthetic crystals — which makes it possible to use large-size synthetic crystals as raw materials that are defect-free and have a high Q value*3 suitable for photolithographic processing.

2. High-precision wafer processing technology
By skillfully combining Kyocera Kinseki's unique technology for high-precision cutting and lapping of synthetic crystals, the thickness of the wafer — which determines the frequency of the AT-cut crystal unit — can be realized with extremely high precision (flatness and parallelism), on the order of nanometers.

3. High-level design technology
To contain the oscillation energy in the crystal element, Kyocera Kinseki uses advanced design and assessment technologies to form the crystal element in specific elliptical and mesa shapes — which is successful in keeping the CI value low.

Elliptical and Mesa Shapes Unique to Kyocera Kinseki
Top and bottom surfaces:
elliptical shape
Side surface (cross-section):
mesa shape
Image:Top and bottom surfaces Image:Side surface (cross-section)

*1 Machine lapping process: Process in which materials are lapped with a cutting tool or a machine tool.
*2 Mesa shape: Mesa means a tabular plateau formed by differential erosion. Derived form this word, the cross-section processed in a convex shape through etching and other processes is known as a mesa shape.
*3 High Q value: A high Q value (quality factor), which indicates ease of oscillation, indicates that the material characteristics are extremely stable.