Polycrystalline Silicon Cascade Self-luminous Devices in Monolithic Sensing Systems
To obtain faster response time and higher stability for an all-silicon photovoltaic biosensor,we propose a monolithic integrated sensor based on a polycrystalline silicon cascade of self-luminous devices.The sensor integrates a silicon-based light source,a silicon-based optical waveguide,and a photodetector.The use of monolithic integration can theoretically improve the performance of the sensor by structurally minimizing the coupling loss of the different components of the sensor system.The sensor system can be compatible with standard Complementary Metal Oxide Semiconductor(CMOS)processes in order to have properties such as low cost,large-scale manufacturability,and a high degree of integration.This integrated system is different from conventional electrical sensing systems,and we have investigated optical waveguide detection sensing considering the high stability and sensitivity characteristic of optical sensing.Since optical detectors have been developed maturely,we focused on the light source and optical waveguide.To realize the monolithic integrated system,we designed a Cascade Silicon Self-Luminous Device(CSSLD)light source and studied its performance.The light source is the core component of the whole sensing system,and the performance of the sensor largely depends on the efficiency,cost-effectiveness and integrability of this light-emitting element.Firstly,the feasibility of the device structure based on the avalanche breakdown operation mode is verified by modelling the light source with simulation software and simulation experiments of the electric field.Secondly,the CSSLD is tested by 0.35 um CMOS process for wafering,and its electroluminescence spectrum is extracted.Three characteristic peaks are found,which are located at 635 nm,700 nm,and 785 nm,respectively.Through analysis,these phenomena indicate that the photoemission is mainly due to the acceleration of electrons gaining energy under high electric field,which promotes theirs in-band jumps in the conduction band and thus enhances the radiative composite probability.In addition to the light source,we designed a Si3N4 waveguide detection structure which matches the CSSLD.This structure can work based on the principle of evanescent wave detection.When the refractive index of the waveguide cladding layer changed,the total reflection condition of the core layer will be destroyed,and leading to a change in the optical energy at the end of the waveguide,thus achieving the detection purpose.The structure is a strip-shaped multimode waveguide with a total length of 50 μm,and its detection region is located between 20～30 μm along the waveguide.Within this detection region,two strips of Si3N4 waveguides which have the thickness of 0.5 μm are deposited.Simulations by the finite element method show that this structure can detect the materials with refractive indices of 1.7～2.0.The analysis shows that the CSSLD light source and Si3N4 waveguide detection structure can be monolithically integrated together and thus applied to sensing systems,which provides a new avenue for low-cost,scalable and miniaturized monolithic integrated sensors.
Monolithic integratedSilicon-based light sourceSilicon nitride waveguideBiosensorRefractive index sensing
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