Si LEDs that operate in the reverse avalanche mode (Si AM LED) and forward bias (Si FB LED), offer various possibilities for realizing nano and micro biosensors directly on chip. The LEDs operate in 450 - 1100nm wavelength range, can emit up to 100nW of optical power, and can be fabricated in micro and nano dimensions. The dispersion characteristics has been studied for a Si AM LED source that is positioned one micron below silicon surface. Subsequently, a fluidic channel sensor device has been designed using the dispersion characteristics. Hence transmittance and absorption spectra studies of species that flow in a fluidic channel can be studied. Similarly, a waveguide-based sensor device has been designed where a receptor layer is fabricated on a waveguide on chip between a Si AM LED and a Si p-i-n detector. The receptor layer binds preferentially with a defined pathogen, and couples with the evanescent radiation of the waveguide.
A two junction micro p+-np+ Silicon Avalanche based Light Emitting Device (Si AM LED) structure was analyzed in terms of dispersion emission characteristics, resulting in different wavelengths of light (colors) being emitted at different angles from the structure. Si AM LEDs can be integrated in on-chip bipolar RF integrated circuitry at micron and even submicron dimensions and have furthermore modulation frequencies into the GHz rang. As a first analyses, the optical propagation mechanisms were modelled by developing a custom designed EXCEL Progressive Ray Tracing Design Tool. (EPRTDT), whereby the positioning of the optical source, the initial launch direction of a particular optical wave fronts, and the subsequent refraction of planar ray fronts into subsequent layers of different refractive indices, in the structure could be progressively modelled. Subsequently, more exact simulations could be obtained by using an existing advanced simulation tool, RSOFT, as is generally available on the free market. The specific approach enabled the design of basic optical microstructures in a silicon 0.35 micron RF bipolar process, determining the dispersion behavior of propagation at different wavelengths, coupling of radiation into adjacently lying waveguides, determining propagation behavior into different type of waveguides, studying interaction with secondary regions of different refractive index, as well as design specific structures that could propagate radiation vertically out of the micro-structures into free space. The analyses have important applications for the realization of wavelength dispersers, couplers of SiAMLEDs into waveguides, realization of optical link structures on silicon chip, as well as micro vertical emitters of radiation out of the chip.
A two-junction micro p+np+ silicon avalanche-mode light-emitting device (Si AMLED) is analyzed for its dispersion characteristics, which generally resulted in different wavelengths of light (colors) being emitted at different angles from the surface of the device. The SiAMLED is integrated into on-chip bipolar radio frequency-integrated circuitry at micron dimensions. LEDs have high-frequency modulation frequencies reaching into the GHz range. Such devices, which are of micron dimension, operate at 8 to 10 V, 1 μA to 2 mA. The emission wavelength is in the 450- to 850-nm range, emission spot sizes are about 1 μm2, and emission intensities are up to 200 nW . μm − 2. The observed geometrical-chromatic dispersion characteristics range from 0.01 deg / nm wavelength for green radiation at a 5 deg exit angle to the normal of the device to 0.16 deg / nm wavelength for blue radiation at a 60 deg exit angle to the normal of the surface of the device. The high dispersion characteristics of the emitted radiation are attributed to the positioning of the optical source ∼1 μm subsurface to the silicon–silicon oxide interface, as well as to the high-refractive index differences between silicon and the surrounding lower refractive index silicon oxide layers. It is believed that the identified dispersion characteristics will have interesting and futuristic on-chip electro-optic applications for on-chip micro-optical wavelength dispersers, futuristic optical communication demultiplexers, along with on-chip microgas and biosensor applications.
Si Av LEDs are easily integrated in on-chip integrated circuitry. They have high modulation frequencies into the GHz range and can be fabricated to sub-micron dimensions. Due to subsurface light generation in the silicon device itself, and the high refractive index differences between silicon and the device environment, the exiting light radiation has interesting dispersion characteristics. Three junction micro p+-np+ Silicon Avalanche based Light Emitting Devices (Si Av LEDs) have been analyzed in terms of dispersion characteristics, generally resulting in different wavelengths of light (colors) being emitted at different angles and solid angles from the surfaces of these devices. The emission wavelength is in the 450 - 850 nm range. The devices are of micron dimension and operate at 8 - 10V, 1μA - 2mA. The emission spot sizes are about 1 micron square. Emission intensities are up to 500 nW.μm-2. The observed dispersion characteristics range from 0.05 degrees per nm per degree at emission angle of 5 degrees, to 0.15 degrees per nm at emission angles of 30 degrees. It is believed that the dispersion characteristics can find interesting and futuristic on-chip electro-optic applications involving particularly a ranging from on chip micro optical wavelength dispersers, communication de-multiplexers, and novel bio-sensor applications. All of these could penetrate into the nanoscale dimensions.
Advanced 3D CAD and optical simulation software were used to design first
iteration on-CMOS chip MOEMS micro-systems. A Si Avalanche-based LED
and an array of detectors interface laterally with a single arm canti-lever system,
all to be fabricated with CMOS technology. Silicon nitride wave-guides are
used as optical propagation channels offering losses of lower than 1dB.cm-1.
Micro-bending and multi-planing of the wave guiding is possible. Far-field
manipulation of the emitted channel radiation is possible. Mechanically
designed and sensor systems can be added by means of CMOS post processing
techniques. The emission level of the Si CMOS Av LEDs is 10+3 higher than
the detectivity of silicon p-i-n detectors, offering good dynamic range in
detection and data analyses. The mature processing characteristics of CMOS
technology offers high integration possibilities and low cost manufacturing of the
designed systems.
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