Modeling of BDJ and BTJ structures for color detection

Abstract

Two color-sensitive detectors, based respectively on BDJ (Buried Double p-n Junction) and BTJ (Buried triple p-n Junction) structures, have recently been developed in standard VLSI processes. The BDJ structure implemented in a CMOS process can produce two photocurrents, and the photocurrent ratio is a monotone function of the wavelength. The BTJ structure realized in a BiCMOS process gives three band-pass spectral responses, thus allowing trichromatic color detetion. In order to obtain better insight into the behavior of these two structures, and to simulate their characteristics, we have established physical models for photocurrent calculations. The following approach has been adopted: i) calculating drift and diffusion photocurrent components which are produced in different depletion layers and neutral regions of silicon; ii) according to their contributions, determining photocurrents flowing through each buried junction. A computer program can be written for device simulations. The validity of these models has been verified through comparison between simulations and measurements. These models can also be used to study effects of parameters involved in the presented models.

CMOS BDJ detector array with charge preamplifiers for sensitive biochemical analysis

“…5, we can see the rapid decrease of I dark,dj when lowering T. It limits the maximum integration duration t int,max for temperatures higher than -5°C. Thus cooling the detector chip down to -10°C allows a 15-fold increase of t int, max, and leads to significant improvements in MDS min and DR according to (3) and (4). There is little interest in working at temperatures lower than -10°C because I dark,sj becomes a limiting factor of t int,max and it has a weak dependence of temperature.…”

“…For photodetection, only the n-well output (well channel) is read, while for wavelength detection, both outputs should be read simultaneously. By using a physically-established model [4], we can evaluate the spectral characteristics of the detector (such as its spectral response η(λ) and its ratio of photocurrents) and their dependence on process parameters.…”

Color Sensors and Their Applications

“…Unfortunately, the spectral responses of this device are not as suitable (for color discrimination) as those of the previous SEG-based device. Nevertheless, the peak responsivities values for the B, G, and R output response curves were about half, comparable to, and twice as large than those provided by a CCD with identical corresponding color filters with 40% peak transmission, respectively [107].…”

“…Thus, the doping profiles and reverse bias conditions of the junctions were tailored by using TCAD process and device simulators (TSUPREM-IV and PISCES-2B), respectively [105]. M. Ben Chouikha et al [106,107] have also proposed a npnp triple-junction structure for color detection that could be implemented with bipolar or BiCMOS technology. The peaks of the three spectral response curves were situated at~480, 530, and 770 nm, respectively.…”

Triple-junction colour sensor fully compatible with CMOS technology: results of a test chip

“…Of course, in order to find a convenient trade off between the desired sensor characteristics, which are dependent on the junction depths, and the isolation prop erties of the pchannel stop, the pstop implantation dose should be carefully chosen. To this purpose, extensive process and device simulations have been carried out by using the 2D simulation programs DIOS and DESSIS, included in the ISETCAD software padiage [9]. As criteria of choice to define the optimum p-stop implantation dose; the threshold voltage, V,,, of a parasitic n-channel trmsistor having the field oxide as a gate insulator hss been considered, together with the depth of the two upper junctions (N+/P-Base and P-Base/N-Well).…”