Meta-optic commercialization and manufacturing readiness is an important topic as optics designers begin evaluating meta-surfaces into optics modules. Moxtek has established a volume production line for visible and NIR wavelength meta-optics with a manufacturing readiness level 8. This provides a unique environment to evaluate the uniformity and capabilities of meta-optic manufacturing techniques. With a statistically significant dataset, mild variations in design concept and lens characteristics can be easily highlighted. We will present baseline MTF and efficiency data related to a variety of metalens characteristics. The goal is to highlight unique meta-optic characteristics that impact performance in volume production. Moxtek has manufactured and characterized metalenses in a wide range of wavelengths, lens diameter, and focal lengths.
Moxtek has attained the required feature fidelity for visible wavelength metalenses through e-beam lithography based mastering for a Nanoimprint Lithography (NIL) and Nb2O5 etching based manufacturing process. An overcoat is also added to the metalenses, which boosts performance and protects against handling damage. Metalens and associated test structure metrology results including MTF, veiling glare, and efficiency will be presented for various designs spanning the visible wavelength range with NA’s varying from 0.02 to 0.71. Collectively, Moxtek has demonstrated volume manufacturing of metalenses for the visible regime, which was made possible by high precision NIL and Etch processes.
Meta-optics have been gaining momentum in the last few years. The meta-atoms for IR range applications are large enough and can be patterned by traditional semiconductor lithography. Making meta-optics in the visible range of 400 to 600nm, the meta-atom structures become too small and the optical lithography falls short. Moxtek has established a manufacturing line enabled by nanoimprint lithography (NIL) that can pattern and build visible range meta-optics. This process has shown proven total efficiency greater than 90% at 532nm wavelength on a baseline over multiple lots. This data set for visible meta-optics, confirms that volume manufacturing of visible wavelength metalens is possible and the patterning barrier has been removed.
AR/VR headsets operating in visible wavelengths require extremely compact and lightweight optics to allow for all day wearable comfort and functionality. This means that visible metalenses would be ideal for this application. Visible metalenses have not been available for volume production until now.
With proven visible metalens production the adaptation into applications such as AR/VR are the next step. At Moxtek, we have an established baseline visible meta-optic process line that provides greater than 90% total efficiency on a lot to lot average.
Moxtek is uniquely positioned to support application development with design validation and production ready nanoimprint masters all processed on high volume tool sets.
Meta-optics have been built in lab settings for years but not on a commercially viable scale. Using electron beam lithography works well in the lab, but this is not an option for volume manufacturing. Patterning subwavelength meta-atom for visible has been just beyond the capabilities of the high-volume deep UV lithography. Due to this patterning barrier, entry into visible meta-optic volume manufacturing has not yet been possible. Moxtek has overcome this barrier and established a volume process line for visible meta-optics utilizing nanoimprint lithography (NIL). Process stability data to qualify the process line for visible meta-optics, confirms that volume manufacturing of metalenses is possible and the patterning barrier has been removed.
Building visible wavelength metalenses presents significant challenges for nanofabrication due to the high aspect ratio features and tight tolerances required for good performance. The requisite phase profiles often impart dramatic changes in nanostructure fill fraction, which are challenging to pattern via optical lithography. One metasurface of interest is a spatially-varying array of nanopillars ranging in diameter from 70nm - 180nm, with gaps between pillars ranging from 180nm - 70nm. To manufacture this and other metastructured devices in volume, Nanoimprint Lithography (NIL) becomes a key enabling technology due to its demonstrated scalability and ability to reliably replicate nanostructures with extremely tight tolerances, even with variations in local spacing.
Another requirement for building metasurfaces for visible light applications, is the ability to pattern full wafers with good repeatability in high volume. Moxtek has therefore set up a 200 mm diameter manufacturing demonstration, where high aspect ratio nanopillars of varying diameter are etched from high refractive index material in order to make visible wavelength metalenses. In this work, metalenses designed for green light were fabricated with both a square grid arrangement and with a radially periodic arrangement. The metalenses were also given a protective coating and the focusing performance was characterized. The manufacturing process evaluation has three key components: 1) characterize the processing bias (from design dimensions to final nanostructure dimensions) at various stages; 2) monitor process stability and repeatability using metrology test devices distributed over the wafer; 3) characterize and verify functioning optical devices. Collectively, we have demonstrated volume manufacturing of metalenses for the visible regime, which was made possible by high precision NIL and Etch processes.
200 mm diameter wafer-scale fabrication, metrology, and optical modeling results are reviewed for surface plasmon resonance (SPR) sensors based on 2-D metallic nano-dome and nano-hole arrays (NHA's) as well as 1-D photonic crystal sensors based on a leaky-waveguide mode resonance effect, with potential applications in label free sensing, surface enhanced Raman spectroscopy (SERS), and surface-enhanced fluorescence spectroscopy (SEFS). Potential markets include micro-arrays for medical diagnostics, forensic testing, environmental monitoring, and food safety. 1-D and 2-D nanostructures were fabricated on glass, fused silica, and silicon wafers using optical lithography and semiconductor processing techniques. Wafer-scale optical metrology results are compared to FDTD modeling and presented along with application-based performance results, including label-free plasmonic and photonic crystal sensing of both surface binding kinetics and bulk refractive index changes. In addition, SEFS and SERS results are presented for 1-D photonic crystal and 2-D metallic nano-array structures. Normal incidence transmittance results for a 550 nm pitch NHA showed good bulk refractive index sensitivity, however an intensity-based design with 665 nm pitch was chosen for use as a compact, label-free sensor at both 650 and 632.8 nm wavelengths. The optimized NHA sensor gives an SPR shift of about 480 nm per refractive index unit when detecting a series of 0-40% glucose solutions, but according to modeling shows about 10 times greater surface sensitivity when operating at 532 nm. Narrow-band photonic crystal resonance sensors showed quality factors over 200, with reasonable wafer-uniformity in terms of both resonance position and peak height.
Moxtek has leveraged existing capabilities in wafer-scale patterning of sub-wavelength wire grid polarizers into the fabrication of 1D and 2D periodic aluminum plasmonic structures. This work will discuss progress in 200 mm diameter wafer-scale fabrication, with detailed emphasis within the realm of microarray based fluorescence detection. Aluminum nanohole arrays in a hexagonal lattice are first numerically investigated. The nanohole array geometry and periodicity are specifically tuned to coincide both with the excitation of the fluorophore Cy3, and to provide a high field enhancement within the nanoholes where labeled biomolecules are captured. This is accomplished through numerical modelling, nanofabrication, SEM imaging, and optical characterization. A 200mm diameter wafer, patterned with the optically optimized nanohole array, is cut into standard 1x3 inch microscope slide pieces and then subsequently printed with various antigens at 9 different concentrations. A sandwich bioassay is then carried out, using the corresponding conjugate antibodies in order to demonstrate specificity. The nanohole array exhibit a 3-4 times total fluorescence enhancement of Cy3, when compared to a leading commercial microarray glass slide.
The design, characterization, and optical modeling of aluminum nano-hole arrays are discussed for potential applications in surface plasmon resonance (SPR) sensing, surface-enhanced Raman scattering (SERS), and surface-enhanced fluorescence spectroscopy (SEFS). In addition, recently-commercialized work on narrow-band, cloaked wire grid polarizers composed of nano-stacked metal and dielectric layers patterned over 200 mm diameter wafers for projection display applications is reviewed. The stacked sub-wavelength nanowire grid results in a narrow-band reduction in reflectance by 1-2 orders of magnitude, which can be tuned throughout the visible spectrum for stray light control.
Broad and narrow-band wire grid polarizer (WGP) products suitable for MWIR and LWIR applications requiring high contrast were developed on antireflection (AR) coated silicon using Moxtek nanowire patterning capabilities. Accurate metrology was gathered in both transmission and reflection from the SWIR to LWIR using a combination of FTIR and dispersive spectrometers, as well as laser-based light sources. The WGP structures were analyzed using SEM, FIB, and STEM techniques and optical data was derived from IR VASE, transmission, and reflectance measurements. Modeling of device performance was achieved using rigorous coupled wave analysis. Laser damage thresholds were determined and various damage mechanisms identified.
High contrast wire grid polarizers on silicon suitable for mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) applications have been developed using wafer-scale aluminum nanowire patterning capabilities. The 144 nm pitch MWIR polarizer typically transmits better than 95% of the passing polarization state from 3.5-5.5 microns while maintaining a contrast ratio of better than 37dB. Between 7 and 15 microns, the broadband LWIR polarizer typically transmits between 55 and 90% of the passing state and has a contrast ratio better than 40 dB. A narrowband 10.6 micron polarizer shows about 85% transmission in the passing state and a contrast ratio of 45 dB. Transmission and reflection measurements were made using various FTIR spectrometers and compared to RCWA modeling of the wire grid polarizer (WGP) performance on antireflection-coated wafers. Laser Damage Threshold (LDT) testing was performed using a continuous wave CO2 laser for the broadband LWIR product and showed a damage threshold of 110 kW/cm2 in the blocking state and 10 kW/cm2 in the passing state. The MWIR LDT testing used an OPO operating at 4 microns with 7 ns pulses and showed LDT of 650 W/cm2 in the blocking state and better than 14 kW/cm2 in the passing state
Moxtek has developed a high contrast IR polarizer on silicon suitable for long wavelength thermal IR applications using our aluminum nanowire, large area patterning capabilities. Between 7 and 15 microns, our 144 nm pitch polarizers transmit better than 70% of the passing polarization state and have a contrast ratio better than 40 dB. Transmission and reflectance measurements were made using a Fourier Transform Infrared (FTIR) spectrometer with instrument accuracy verified using silicon and germanium reference standards. Results were compared to RCWA modeling of the wire grid polarizer (WGP) performance on antireflection-coated wafers. The FTIR instrument noise floor limited the maximum contrast measurement to about 40 dB, but high polarizer contrast was verified at 10.6 μm using a CO2 laser and pyroelectric detector. A continuous wave Gaussian beam from a CO2 laser was used for Laser Damage Threshold (LDT) testing and showed LDT values of 110 kW/cm2 and 10 kW/cm2 in the blocking and passing states respectively. Analysis of laser damage threshold test samples shows the damage propagating from defects in the anti-reflection (AR) coating. Removing these AR coating defects should improve LDT performance and transmission in the thermal IR.
KEYWORDS: Resistance, Bolometers, Sensors, Prototyping, Digital electronics, Electronics, Temperature metrology, Semiconductors, Detector arrays, Control systems
Integration of detector arrays and digital CMOS circuitry can confer significant performance improvements on an imaging system. In this paper we present an integrated sensor array based on (Figure 1), micro bolometer (MB) elements deposited on a CMOS substrate containing electronics for random access readout, amplification, gain and offset control and digitization. Such integrated MB arrays are effective components in a novel implementation of an earth-horizon attitude sensor for satellites. The bolometer elements are used to distinguish the earth's thermal IR from the space background. For this application, the reduced detectivity of MB arrays compared with cooled IR detectors can be tolerated. Low mass, enhanced reliability, and low power consumption are gained by using an uncooled IR detector, and by using an integrated circuit design. These considerations are especially important for microsatellites. The low cost per array facilitates the use of multiple arrays, which allows significant flexibility in the optical and systems designs. The integrated chip design allows for random-access readout, on-chip gain and offset compensation and local control of pixel geometry, which contribute to the overall system effectiveness and help to allay any performance reductions that come from reduced detectivity.
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