Can somebody tell me, which bond gets formed at Glass Kovar interface, in
Anodic bonding of Kovar to Glass.

Ashwini

On Thu, Oct 2, 2008 at 9:01 PM, Brubaker Chad wrote:

> That kind of anodic bond is definitely possible - the general elements for
> the physics still exist.  The requirement is that a certain amount of
> current be achieved to cause sodium migration away from the bond interface.
> The biggest limitation will be the resistance of the oxide.  Luckily, the
> resistance of the oxide is a function of temperature.
>
> At room temp, SiO2 has a resistivity of ~1E13 ohm-m.  But at 600C, that
> drops to ~70,000 (and all the way to .004 at 1300ºC).  Using a power based
> function (only an approximation, but the closer to known values, the more
> accurate it is), we can estimate 200,000 ohm-m at 500ºC, or 650,000 ohm-m at
> 400ºC.
>
> Now, one thing to keep in mind - resistance is resistivity /area.  However,
> as we are primarily concerned with current flux (since current will increase
> with the area of the wafer), resistivity is the best term to use.
>
> At 200,000 ohm-m, .5 µm of oxide will provide 1000 ohm-m2 of resistivity.
>  Using a 2000V potential, assuming the oxide resistance is dominating
> initially, this would still allow a current density in the initial stages of
> the bond of2A/m2, which is sufficient for anodic bonding (this translates to
> 63mA for a 200mm wafer - definitely well within bondable range).
>
> If we lower the bonding temperature to 400ºC, then the current flux drops
> to .61A/m2 - the bond may work at this point, but I wouldn't be sure.