Integrated Photodiodes in Standard CMOS Technology for CD and DVD Applications

The influence of two different geometries (layouts) and two structures of high-speed photodiodes in fully standard 0.18 μm CMOS technology on their intrinsic (physical) and electrical bandwidths is analyzed. In addition, a possible application of the integrated photodiodes for the CD and DVD optical pick-up units is discussed. Two photodiode structures with a highest responsivity are studied: nwell/p-substrate and p+/nwell/p-substrate (double photodiode). The photodiode bandwidths are compared for λ=780 nm and λ=650 nm wavelength, corresponding to the lasers for CD and DVD, respectively. Slow substrate current component limits the intrinsic bandwidth of nwell/p-substrate and p+/nwell/p-substrate photodiodes to 6MHz and 7MHz, for a CD application as well as 70MHz and 100MHz for a DVD application. The electrical bandwidth of these diodes in combination with typical transimpedance amplifiers, will be always larger than the calculated intrinsic bandwidths meaning that the diode capacitance is not critical in total photoreceiver design