AN3169

Triac technologies and immunity

Doc ID 17194 Rev 1

3/12

Figure 3.

“Top” glass technology

Both top and mesa glass technologies are very cost effective. The insulation capability of

glass is very high. This helps to achieve high voltage devices with a limited periphery area.

Mesa glass technology is the cheaper one as this technology uses less silicon area to

withstand reverse voltage. For top technology, the reverse PN junction is terminated on the

upper side of the die thanks to the deep P well. Such dies are bigger for the same active

area than mesa dies. This is the reason why top technology is mainly used for low current

Triacs.

Unfortunately it is not possible to ensure a good operation of a die with glass passivation

voltage reaches the breakdown value, a current will flow through the die periphery, causing

heat dissipation at the glass-silicon interface. This heat could cause mechanical stress and

damage this interface. The device could then be damaged.

To develop switches able to work up to their breakdown voltage, a planar technology has to

be implemented. Such a technology uses photolithography to terminate the PN junction at

the top of the die, and oxide passivation instead of glass (see Figure 4). There is no more

glass-silicon interface issue. ACST devices use this kind of technology (see Reference 4).

Figure 4.

Planar technology

N+

P

N

P

N

N

N

P

Cathode

Anode

Metalization

Gate

Glass

Metalization

P

N

Cathode

Gate

Anode

P

N

P

Oxyde

Passivation

N

N

P

N

P

N

N

P

N

N