Proceedings Article | 12 September 2007
Proc. SPIE. 6659, Organic-based Chemical and Biological Sensors
KEYWORDS: Thin films, Photodetectors, Sensors, Organic light emitting diodes, Glasses, Silicon, Electroluminescence, Oxygen, Plasma enhanced chemical vapor deposition, Palladium
Steps towards the improvement of a compact photoluminescence (PL)-based sensor array that is fully structurally
integrated are described. The approach is demonstrated for oxygen sensing, which can be monitored via its effect on the
PL intensity I or decay time τ of oxygen-sensitive dyes such as Pt octaethylporphryn (PtOEP) and its Pd analog
(PdOEP). The integrated components include (1) an organic light emitting device (OLED) excitation source, which is an
array of coumarin-doped tris(quinolinolate) Al (Alq3) pixels, (2) the sensor film, i.e., PdOEP embedded in polystyrene,
and (3) the photodetector (PD), which is a plasma-enhanced CVD-grown p-i-n or n-i-p structure, based on amorphous or
nanocrystalline (Si,Ge):H. These components are fabricated on common or separate substrates that are attached back-to-back,
resulting in sensors with a thickness largely determined by that of the substrates. The fully integrated oxygen
sensor is demonstrated first by fabricating each of the three components on a separate substrate. The PD was placed in
front of a flow cell containing the sensor film, while the OLED array was "behind" the sensor film. This design showed
the expected trend in monitoring different concentration of O2 via their effect on I, with improved detection sensitivity
achieved by shielding the electromagnetic noise synchronous with the pulsed OLED. The detection sensitivity using the
I monitoring mode is expected to further increase by reducing the OLED tail emission. The issue of the OLED
background can be eliminated by monitoring the oxygen concentration via its effect on τ, where the OLED is pulsed and
τ is measured while the OLED is off. Steps therefore focused also on shortening the response time of the PDs, and
understanding the factors affecting their speed. Development of a sensor array, where the PD pixels are fabricated
between the OLED pixels on the same side of a common substrate, is also discussed.
