Mumbai University > Electronics Engineering > Sem 8 > MEMS Technology

Marks: 4M

An alternative method, which is restricted to certain glases bonded to conductors is called field – assisted bonding or anodic bonding.

The mechanism responsible for anodic bonding is the mobility of sodium ions in the glass.

e.g. Pyrex 7740 glass having thermal expansion close to that of silicon.

When the silicon wafer is placed on the glass and turns are heated to temp. around 5000 C a positive voltage (300-700V) applied to the silicon repels sodium ion form the glass surface. Creating a net negative charge at the glass surface.

The force of attraction between the positively charged silicon wafer and the negatively charged glass surface brings the two surfaces intimate contact and at high tepm, they can fuse together.

Contact is typically initiated at a single point by applying a load, and as contact is established it spreads out to cover the rest of the wafer.

Bonding time ranges from seconds to minutes and can be monitored by measuring the current in the circuit. When bonding is completed this current drops to zero.