SPR Based Integrated Chemical Sensor

Chemical sensors are used in many industries; from medical to homeland security. These industries demand sensors to be high sensitivity, low cost, and small size. Surface plasmon resonance (SPR) chemical sensor provides a promising solution to this problem. SPR is a phenomenon that causes extraordinary transmission in periodically textured metal membranes. These periodically modified metal membranes are called photonic crystals. The presence of a high refractive index chemical on the metal membrane will cause a spectral shift in the transmission peaks. Each chemical has a unique dielectric constant that can be detected from a photodiode’s electronic signal. An array of nanoholes is fabricated on a 100 nm Ag membrane deposited on top of a pn photodiode. By varying the lattice constants in the array the dielectric constant of a chemical contaminant can be identified by observing which crystal is experiencing enhanced transmission. Different lattice constants will be tested to find the optimal settings which produce the largest and most sensitive electronic signal. The electronic signal is proportional to the photocurrent and displayed on a LCD monitor. The LCD monitor is onboard along with the photonic crystal arrays and power supply. This allows the sensor to be portable. The processing of that electronic signal to the LCD monitor must be engineered in a size and power efficient manner while maintaining high sensitivity. The prototyping of such a device includes optical testing, board design, as well as device assembly and programming to interface with a microcontroller. The fabrication of SPR chemical sensors is mostly compatible with the CMOS process. As the cost and the critical dimension of CMOS processing continue to decrease, the proposed method offers a pathway to a lower cost, more portable, more functional, and even personalized sensor chip