A CMOS Luminescence Sensor for Intensity and Lifetime Dual Sensing

摘要

Luminescence is an important phenomenon in nature used extensively in biology, life sciences, biomedical and environmental applications. It is the light emitted by a substance not resulting from heat after absorbing a certain amount of excitation energy. Measurements of luminescence could involve measuring its intensity or measuring its lifetime. Sensing based on luminescence intensity suffers from the variation of many factors such as the optical path, excitation light intensity and the concentration of luminescent indicator used. Instead, sensing using luminescence lifetime is more reliable as it is immune to these factors. Both luminescence intensity and lifetime detection techniques can be applied to luminescence-based optical sensors since the emission intensity and lifetime of the luminescent indicator varies as a function of the concentration of a certain substance in the environment.;In this dissertation, we propose a CMOS (complementary metal-oxide-semiconductor) sensor that combines both luminescence intensity and lifetime detection on a single chip. It applies multi-cycle charge modulation for lifetime extraction realized by capacitive transimpedance amplifier (CTIA) based circuitry. The designed in-pixel CTIA-based structure is able to capture the weak luminescence-induced voltage signal by accumulating photon-generated charges in 25 discrete gated 10ms time windows and 10us pulse width. A pinned photodiode on chip with 1.04pA dark current is utilized for luminescence detection. The proposed CTIA-based circuitry can achieve 2.1 mV/(nW/cm2) responsivity and 4.38 nW/cm2 resolution at 630 nm wavelength for intensity measurement and 45 ns resolution for lifetime measurement. The sensor chip is employed for measuring time constants and luminescence lifetimes of an InGaN-based white LED at different wavelengths. In addition, we demonstrate accurate measurement of the lifetime of an oxygen sensitive chromophore with sensitivity to oxygen concentration of 7.5%/ppm and 6%/ppm in both intensity and lifetime domain. This CMOS enabled oxygen sensor was then employed to test water quality from different sources (tap water, lakes, and rivers). However this sensor required an external analog to digital converter and, its operation was restricted to a dark room due to the sensor saturation caused by ambient light.;In order to solve these issues, an improved CMOS image sensor for luminescence imaging was also designed. In addition to the combined intensity and lifetime sensing feature, this new image sensor converts the integrated output voltage into digital pulses. Ambient light compensation is also realized with an on-chip charge-pump based compensation circuitry. Driven by a 10 KHz clock signal with 20 us pulse width as the integration time window, the proposed circuitry can achieve 93 Hz/(uW/cm2) responsivity and 19nW/cm 2 resolution at 575 nm. 2D luminescence images of a white LED are obtained with this proposed image sensor.;Since common luminophores may exhibit different lifetimes one can use lifetime as a means of discriminating them. This enables the paradigm of "filterless" imaging. We verify this hypothesis for filter-less imaging for two fluorescent samples with similar emission wavelength ([Ru(dpp)3Cl2] and [Ru(bpy)3Cl2]) but different lifetimes. According to the measurement results, the proposed image sensor can easily distinguish two fluorescent indicators. Benefiting from this feature, in addition to the dual sensing of fluorescence intensity and lifetime, the proposed CMOS image sensor has the potential to be used in fluorescence imaging systems applying multiple fluorescent indicators without selective optical filters.