Wavelength detection with integrated filter-less BiCMOS RGB sensor

Abstract

A filter-less BiCMOS RGB colour sensor for wavelength detection in the wavelength range from 400 to 900 nm is presented. The sensor is based on the effect that light with longer wavelength penetrates silicon deeper than light with shorter wavelength. The detector is formed by three vertically stacked photodiodes: a deep diode used as the sensing element for red light, a middle diode to detect green light and a shallow diode as the blue light detector. The resulting RGB output is used to accurately determine the wavelength of the incident light. The sensor is fabricated in standard 0.6 mm BiCMOS technology without any process modifications.Introduction: Most conventional CMOS colour sensors are based on at least three photodetectors covered with RGB printed Bayer filters or interference filters. The three detectors themselves are inherently intensity detectors but have no colour selectivity. To add colour selectivity each detector is covered with a certain colour filter and records one distinct colour. The wavelength of the incident light is identified by combining the output signals of the three neighbouring detectors [1]. A major drawback of such tristimulus colour sensors is the need for additional filters and the increase of silicon area which adds to production costs.Filter-less RGB colour sensors with vertically arranged pn junctions (e.g. as described in [2,3]) eliminate these disadvantages. To our knowledge, however, such detectors have not yet been used for wavelength detection. In this Letter, we describe the accurate wavelength determination with three vertically-stacked photodiodes (two of them using the n+ buried layer) in a standard BiCMOS technology without any additional production steps.

A Multifunction Heterojunction Formed Between Pentacene and a Single‐Crystal Silicon Nanomembrane

“…The relatively low photo responsivity of the p‐n diode is because the SiNM is very thin. Low photoresponsivity and η EQE could be further improved by applying thicker SiNM or reflector layer on the plastic substrate 29, 30…”

Investigation of transient photocurrent response of triple pn junction structure

“…For 520nm light, we are mainly concerned with the rise and fall time of the photocurrent in the middle photodiode, even though all three pn junctions exhibit photogenerated current. Ideally, the bottom pn junction should not exhibit any response to green light, but fortunately the responsivity of the bottom pn junction is only half as large as the responsitivity of the middle pn junction for 520nm [4]. The rise and fall times of the photocurrent in the middle photodiode are 23.5 ns and 20.9 ns, leading to a maximum data rate of 30 Mbit/s.…”

“…Then, a triple‐junction colour sensor fully compatible with CMOS technology was introduced [3]. A filter‐less multicolour photodetector using standard BiCMOS technology was reported [4]. With this structure, the colour detector achieved high compactness and the complexity of the chip was reduced.…”

High‐Accuracy and Broadband Wavelength Sensor with Detection Region Ranging from Deep Ultraviolet to Near Infrared Light

“…[11] As an important complement to above filter-assisted wavelength sensors, filterless sensor has lately received increasing research interest as well. [12][13][14] Although this device can quantitatively discriminate the wavelength of incident light, they are however characterized by relatively narrow sensing range and complicated device structures which entail very sophisticated instrument during device fabrication process. [15][16][17][18][19][20] Thereby, high-resolution wavelength sensor with simple device geometry is in great demand.Various study have shown that photodetectors composed of artificial nanostructures in the form of nanofilm or nanowires can exhibit unique optoelectronic characteristics.…”