Browse Prior Art Database

Poly diode triggered Silicon Controlled rectifier (SCR) Clamp

IP.com Disclosure Number: IPCOM000241141D
Publication Date: 2015-Mar-31
Document File: 5 page(s) / 161K

Publishing Venue

The IP.com Prior Art Database

Abstract

Different applications require different voltage swings to be tolerated on the signal or power line. Hence tunable trigger voltage is very important for the ESD protection device to be versatile.The turn on voltage of an SCR by itself (called the breakdown configuration is not tunable. However an external circuitry can be used to aid the positive feedback mechanism in order to tune the turn on (or trigger) voltage. Various configurations are used as trigger circuits for the SCR such Diode Triggered SCR (DTSCR), and Grounded Gate Triggered SCR (GGSCR).

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 51% of the total text.

Page 01 of 5

Poly diode triggered Silicon Controlled rectifier (SCR) Clamp


Silicon controlled Rectifier (SCR) is a device often used in on chip ESD protection. Owing to its large off resistance, snapback characteristics, and very low ON resistance, and relatively high turn on voltage, it offers excellent protection against ESD zaps in applications where high voltage swing is required. SCR uses two BJTs in a positive feedback configuration in order to achieve snapback.

Different applications require different voltage swings to be tolerated on the signal or power line. Hence tunable trigger voltage is very important for the ESD protection device to be versatile.The turn on voltage of a SCR by itself (called the breakdown configuration

) is not tunable. However an external circuitry can be used to aid the positive feedback mechanism in order to tune the turn on (or trigger) voltage. Various configurations are used as trigger circuits for the SCR such Diode Triggered SCR (DTSCR), and Grounded Gate Triggered SCR (GGSCR).

1


Page 02 of 5

These methods have their own advantages and disadvantages. The DT, in particularly is very useful because of its ease in tuning the trigger voltage of the SCR. The trigger voltage is dependent on the number of diodes used in the trigger circuit. The diode string used to tune the trigger voltage shares a common substrate. Hence this arrangement is prone to suffer from current gain similar to a darlington pair. Due to the inherent current gain due to a common substrate, the trigger voltage cannot be tuned linearly with number of diodes (Vtrigger ends up less being than number of diodes times diode knee voltage). Further the diodes laid out with the SCR device take up extra area on the silicon. The high area required can be problem particularly if a diode string with a large number of diodes is used to achieve high trigger voltage.

In order to tackle the two problems mentioned above, we propose the use of poly-diode string as the trigger diode for the DTSCR.

Poly-diodes do not share a common substrate with each other due to the presence of oxide below and therefore, the problem of current gain can be avoided. This will ensure a good scalability of trigger voltage with respect to number of diodes used. Hence higher trigger voltages (more than a couple of volts) can be easlily achieved compared with any of the configurations mentioned earlier.

Further, the poly-diodes can be laid out directly over the SCR device, resulting in considerable area savings...