Online proceedings - EDA Publishing Association

11-13
May 2011, Aix-en-Provence, France
and where the Cr particles act as quenchers of fluorescence
V4 V3 V2 V1
similarly to TiO 2 [8].
It should be mentioned that the absorbing filter must be
implemented with low-autofluorescence materials (see
autofluorescence measurements of different polymeric
p+
materials in Fig. 1). Our measurements show that the
I1
autofluorescence of our chosen material combination,
n-base
I2
KMPR/Orasol, is low, comparable to that of glass substrate.
P-Well
I3 Deep N-Well
B. CMOS BMJ (Buried Multiple pn-Junction) structure
I4 P+ substrate
Integrated BMJ photodetectors such as BDJ and BTJ
Fig. 2 BQJ a) structure b) Chip micrograph
(Buried Double/triple pn-Junction) have been reported [9-
10]. These devices feature two or three photodiodes in
stacked form and have an aggregate spectral response
covering the visible and near-IR ranges [11]. These BMJ
can thus be operated for photodetection like a photodiode,
but with a more sensitive response owing to signal
contributions from the multiple photodiodes. In addition,
the wavelength-sensitive characteristics of BMJ detectors
are particularly interesting for spectral discrimination.
When measuring a ratio between two signals from the C. Process Integration
stacked photodiodes, it is possible to distinguish different
fluorescence spectra, and in cases of biochemical analysis,
to lead to molecular identification. Such detection does not
require dispersive optical devices such as gratings, and is
particularly suitable for low-level fluorescence [4].
With an increased number of stacked photodiodes, the
spectral sensitivity as well as the capability of spectral
discrimination of the BMJ detector can be improved. Thus
we propose a BQJ (Buried Quad pn-Junction) detector that
has been designed and fabricated using the Teledyne-
DALSA (Bromont, Canada) C08G 0.8 μm multi-high
voltage CMOS/DMOS process.
The proposed BQJ photodetector structure (Fig. 2)
consists of four stacked buried junctions consisting of a
I3 + I4
I2 + I3
I1 + I2
I1
shallow p+-diffusion/n-base well junction (J1), a deeper P-
Well/n-base junction (J2), a P-Well/Deep N-Well junction
(J3) and P+ substrate/Deep N-Well junction (J4),
respectively. It has 4 outputs allowing bias setting of the
buried junctions and signal readout. Simple processing of
these output signals determines the 4 photodiodes currents
(I 1 , I 2 , I 3 and I 4 ) as well as their sum.
For monolithic integration of a hybrid optical filter with
the BQJ photodetector, we have experimented with two
CMOS post-processing approaches. The first one consists in
depositing the hybrid filter directly onto the packaged
CMOS die (see Fig. 3). Though this technique is not
compatible with industrial processes, it is nevertheless a
convenient lab approach to validate the performance of our
integrated hybrid filters on BMJ photodetector.
The interference filter (thickness: ~ 1.2 µm) can be
deposited onto a packaged CMOS BMJ photodetector as
shown on Fig. 5. The interference filter was designed using
the Essential Macleod software (Thin Film Center Inc.).
The second step of this integration is the deposition of the
absorbing component (thickness: ~ 1.6 µm) by spin-coating.
An alternative process integration approach is to deposit
the hybrid filter directly on a CMOS wafer, while protecting
the PAD interconnections for use of the device under a
probing station or for interconnects in a standard package.
Fig. 1 Autofluorescence measurements of the various candidate materials for
use as an absorbing filter.
Fig. 3 Hybrid filter (integration of the interference filter shown into the
inset) on BDJ photodetector packaged in DIP-28 package.
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