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Base Window Defined Schottky Diode for NPN Transistor Clamping

IP.com Disclosure Number: IPCOM000088245D
Original Publication Date: 1977-May-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 55K

Publishing Venue

IBM

Related People

Chang, AW: AUTHOR [+2]

Abstract

In the application of high speed logic gate design, Schottky metal-Si contact diodes (SBD) are often employed between the NPN transistor base-collector junctions. They are shown as clamping diodes SBD-1, SBD-2, SBD-3 for the DTL gate (Fig. 1) and the TTL gate (Fig. 2), where E, B and C are the emitter, base and collector contacts, respectively, for transistors, T, resistors R1, R2 and R3 and voltage supply VP. SBD-4 is an input diode which does not have the problem herein described. It is important that the physical size and the metal-Si composition in the whole region of the SBD area stay controlled and integrated.

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Base Window Defined Schottky Diode for NPN Transistor Clamping

In the application of high speed logic gate design, Schottky metal-Si contact diodes (SBD) are often employed between the NPN transistor base-collector junctions. They are shown as clamping diodes SBD-1, SBD-2, SBD-3 for the DTL gate (Fig. 1) and the TTL gate (Fig. 2), where E, B and C are the emitter, base and collector contacts, respectively, for transistors, T, resistors R1, R2 and R3 and voltage supply VP. SBD-4 is an input diode which does not have the problem herein described. It is important that the physical size and the metal-Si composition in the whole region of the SBD area stay controlled and integrated.

Conventional diode design often has a portion of its periphery defined by silicon dioxide. Therefore, when the SBD contact, such as Pt-Si, is exposed to any silicon dioxide removal processes, new Si area along the diode edges may be fonmed. Post-contact metallurgy that covered the new area would form a parasitic diode in parallel with the original diode. The composite device often exhibited undesirable characteristics, such as shorting or leakages at low voltage levels.

The design in Figs. 3A and 3B uses the base-diffusion shape with a "void" in which the SBD 12 is formed. The "void" region 10 is a portion of the N- epitaxial layer. All of its four sides are guardbanded by P+ diffusions. The base contact window 14 is greater than the SBD shape 12. In this manner, the SBD area is defined by...