Photonic circuits integrated with CMOS compatible photodetectors Dana Cristea a, * , F. Craciunoiu a , M. Modreanu a , M. Caldararu b , I. Cernica a a National Institute for R & D in Microtechnologies, P.O. Box 38-160, 72225 Bucharest, Romania b ECOSEN Ltd., 73101 Bucharest, Romania Abstract This paper presents the integration of photodetectors and photonic circuits waveguides and interferometers, cou- pling elements and chemo-optical transducing layer) on one silicon chip. Dierent materials: silicon, doped or undoped silica, SiO x N y , polymers, and dierent technologies: LPCVD, APCVD, sol±gel, spinning, micromachining have been used to realize the photonic and micromechanical components and the transducers. Also, MOS compatible processes have been used for optoelectronic circuits. The attention was focused on the matching of all the involved technologies, to allow the monolithic integration of all components, and also on the design and fabrication of special structures of photodetectors. Two types of high responsivity photodetectors, a photo-FET and a bipolar NPN phototransistor, with modi®ed structures that allow the optical coupling to the waveguides have been designed and experimented. An original 3-D model was developed for the system: opto-FET-coupler-waveguide. A test circuit for sensor applications was experimented. All the components of the test circuits, photodetectors, waveguides, couplers, were obtained using CMOS-compatible processes. The aim of our research activity was to obtain microsensors with optical read- out. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Photonic integrated circuits; Photodetectors; Waveguides; Microsensors 1. Introduction The possibility of combining photonic, elec- tronic and micromechanical components on a sil- icon chip is a strong motivation for Si-based photonic integrated circuits and microsystems [1±4]. We developed components waveguides, interferometers, photodetectors, micromechanical structures) and subsystems for sensor applications. This paper presents the design, modeling and ex- perimental realization of the optoelectronic and photonic components and circuits for microsen- sors, underlining the original approaches and re- sults. For sensor application, photodetectors with high optical sensitivity are required. That is why we designed special structures of high gain pho- todetectors that allow optical coupling with waveguides and monolithic integration with elec- tronic and photonic circuits. As these photode- tectors have non-standard structures, original models were developed. Also new materials and processes were studied and experimented in order to improve the component performance. Then the possibility of including the technological steps for waveguides, coupling elements, micromechanical structures and transducing layers was analyzed Optical Materials 17 2001) 201±205 www.elsevier.nl/locate/optmat * Corresponding author. Tel.: +40-1-4908412; fax: +40-1- 4908238. E-mail address: danac@imt.ro D. Cristea). 0925-3467/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0925-346701)00045-3