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Browse Prior Art Database

Simple Method of Reducing Parasitic Pad Capacitance in Ridge Lasers

IP.com Disclosure Number: IPCOM000036539D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 76K

Publishing Venue

IBM

Related People

Deutsch, U: AUTHOR [+3]

Abstract

The area of bonding pads of typical semiconductor lasers is large compared with the active area of the laser. The parasitic capacitance of these pads is in parallel with the laser and limits its high frequency response. Proposed is a way of reducing this parasitic capacitance by placing the bonding pads on a thick, insulating spacer of low dielectric constant. The described method is compatible with a photoresist-based ridge-etch procedure which allows the contact openings in the insulator to be self-aligned to the ridges.

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Simple Method of Reducing Parasitic Pad Capacitance in Ridge Lasers

The area of bonding pads of typical semiconductor lasers is large compared with the active area of the laser. The parasitic capacitance of these pads is in parallel with the laser and limits its high frequency response. Proposed is a way of reducing this parasitic capacitance by placing the bonding pads on a thick, insulating spacer of low dielectric constant. The described method is compatible with a photoresist-based ridge-etch procedure which allows the contact openings in the insulator to be self-aligned to the ridges.

Fig. 1 shows a cross-section of a ridge laser during fabrication of the ridge and the deposition of the thick insulating spacer. The process of providing the photoresist mask is standard. The ridge is then wet-etched, causing the undercut shown in Fig. 1(a). A thick, low stress coating of SiO2 is then deposited using a low temperature (100 oC) plasma enhanced chemical vapor deposition (PECVD) process. During the deposition, self-shadowing of the growing film occurs (region A, Fig. 1(b) which prevents substantial conformal deposition in the corner formed by the photoresist and the etched ridge. This permits lift-off, even of thick layers. After the removal of the surplus SiO2 by lifting off the photoresist, the top contact metal, which also acts as the bonding pad, is deposited (Fig. 1 (c)).

Since the described insulator deposition process takes place at low temperature, it is c...