KDK NEWS

Technology of Inverted Mesa Blank

In the future multimedia society, the computer communications such as Internet will be a majority in the usage of communication lines, and its capacity is expected to be 100 times more than the present by the rapid increase of users and broadbandization of applications. Therefore a substantial communication network which contributes to the advanced information society is necessary. There is an optical communication technology as one of the solutions, and introduction of the wavelength division multiplex (WDM) transmission system that multiplexes optical signals into one optical fiber is rapidly being proceeded. Along with these phenomena, the crystal products are required to be smaller and high-frequency devices. Ten years of study had been done to make thinner crystal base, and unique technology used magnetron plasma etching had been developed several years ago. (Applied for patent)
So far inverted mesa blanks have been manufactured by a wet etching method that utilized chemical reactions for the etching process. However, this method has fatal defects which make etching channels (pin holes) and rough surface, and also the long manufacturing time is not suitable for manufacturing uniformity and mass productivity. In order to solve these problems, the etching process had been developed to produce thinly etched crystal blanks by using magnetron plasma apparatus utilized an external magnetic field to generate high density plasma by injecting etching gas (CF₄),Ar,O₂ gas into the reactor.

Dry Etching Process

Ordinary crystal products are manufactured by AT-Cut (thickness-shear) method that the temperature-frequency drift is stabilized. (Note 1) The marginal thickness of normal mechanical lapping was approximately 30µm. So magnetron plasma etching process to produce inverted mesa blank had been developed for small and high-frequency crystal devices.

Ex) High frequency resonator

Normal frequency : 167.331645MHz
Frequency stability : ±20ppm
Frequency tolerance : ±20ppm
Operating temperature range : -10~+70
Oscillation mode : Fundamental tone
ESR : 30 Ohm max

Picture of High Frequency Fundamental Resonator (167.331645MHZ)

Note 1: The relation between frequency and thickness
T = ( A x N ) / F
T: Thickness(µm)
A: Constant of Frequency(1670)
N: Oscillation Mode (1, 3, 5,)
F: Frequency(MHz)

Waveform of inverted mesa blank(T=8µm)

Applications
The voltage controlled crystal oscillators (VCXO) called SAT series had been developed for WDM photonics networks.
Sample supply of 622.08MHz, 666.51428MHz and 669.32658MHz for WDM market will be started from 2002.

SAT7250A(VCXO)

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Technical Report (PDF-File)

SAT7000-Series Spec Sheet (PDF-File)