AC response of 0.35 µm CMOS triple‐junction photodetector

Abstract

A vertically stacked triple-junction photodiode (PD) is characterised for its suitability for sensor applications which demand a high speed. The proposed PD is implemented in a 0.35 µm CMOS process without process modifications. The AC performance of the detector is characterised at three wavelengths, blue (410 nm), green (520 nm) and red (675 nm). The measurements are carried out with a high dynamic range to fully characterise possible interactions between the different wavelengths (cross-coupling mechanisms).Introduction: Double [1, 2], triple [3][4][5] or quad [6] junction photodiodes (PDs) are often used in sensor applications where a colour detector is needed. These PDs are formed by stacking two, three or four PD junctions vertically. The wanted colour dependency is based on the wavelength-dependent penetration depth of light in silicon. The basic working principle is well understood and widely published. All these applications have one aspect in common. These applications only need a low-speed PD. However for some applications, the speed of the used PD is also of interest. Only a few published papers focus on this topic. Schidl et al.[4] focuses on the transient response (0.6 µm BiCMOS triple-junction PD) and [3] focuses on the cutoff frequency at one wavelength (90 nm CMOS triple-junction PD). The results in these published papers indicate that there are some interesting properties not fully characterised yet. For instance, one interesting question is whether there is a (capacitive) interaction between the PD junctions at higher frequencies. Therefore, we have chosen to characterise a new 0.35 µm CMOS triple-junction PD in the frequency domain with different wavelengths of the incident light. In this Letter, we quantify the interaction between the different PD junctions and discuss the implications for possible applications of this PD.

A CMOS Buried Quad p-n Junction Photodetector Model

“…It is particularly attractive for multispectral applications, such as color detection, light wavelength characterization and simultaneous spectral analysis of several light sources [3,4,6,7,9,11,12,14,[15][16][17]. It has been also shown that this kind of photodetector is well adapted to optical data communication of more than 100 Mbits/s [18][19][20], where the BMJ photodetectors permit the natural demultiplexing of separate incident light sources.…”

“…In such conditions, the band-to-band tunneling (BBT) is not negligible. Its contribution is formulated from the conventional Zener tunneling equation: (20) where C bbtθ and E 0 are constants that are highly dependent on the device material; the E MAXθ are the maximum electrical fields in each depletion zone.…”

“…Basic CMOS and BiCMOS processes have allowed implementation of buried double junction (BDJ) and buried triple p-n junction (BTJ) device structures [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Using an advanced CMOS technology, we can design and integrate a buried quad junction (BQJ) photodetector for specific applications [23][24][25][26][27][28].…”

“…They model the response's time to generate photocurrents when an incident light suddenly reaches the surface of the photodetector. They are approximated by a first order model and defined by the cut-off frequencies[18][19][20]…”

Characterization and comparison of stacked photodiodes spectral sensitivity in CMOS technology

“…The use of stacked photodiodes for vision sensors has been explored by different authors [6]- [8], [12]. The transient response of these different stacked photodiodes have been analyzed for communications applications; for instance, [13], [14]. Image sensors with stacked diodes are also commercialized by Foveon [11].…”