The overall goal of this procedure is to simulate, fabricate, and characterize a terahertz metamaterial absorber structure. First, perform simulations to establish the optimum metamaterial absorber design. Then fabricate this optimized design.
Next, evaluate the experimental performance of the absorber using Fourier transform infrared spectroscopy. The resulting single band, dual band and broadband ertz metamaterial absorber devices are capable of greater than 80%absorption at the resonance peak. And when coupled with an appropriate sensor, have applications in ertz imaging and spectroscopy.
The technology that we're working on will enable us to make small, portable terahertz imaging systems, which will be handheld by working on Metamaterial technologies, which we hope to integrate with sensors such as barometers, we hope to able to achieve high speed, high sensitivity devices. The implications of this technique extend toward the rapid design simulation, fabrication and characterization of prototype terahertz Metamaterial Devices. Not only does this method demonstrate how to fabricate a telehealth metamaterial absorber can also be applied to the design and fabrication of other metamaterial devices and components such as filters, modulators, perfect lenses and invisibility cloaks.
Follow the simulation section in the journal article protocol to design a metamaterial absorber with the desired absorption spectrum characteristics. Clean the silicon in sequential solutions of optic clear acetone and isopropanol. First immerse in the solvent at 50 degrees Celsius for 10 minutes, and then subject to ultrasonic agitation.
Next, evaporate a metal bilayer of titanium and gold onto the silicon using an electron beam evaporator. Note that the metal thickness must be greater than the skin depth at the desired operating frequency. After cleaning in solvents as described earlier, pipette VM 651 primer onto the sample and leave it to relax for 20 seconds.
Then spin the sample at 4, 000 RPM for five seconds and bake on a contact hot plate at 120 degrees Celsius for 60 seconds. Pipette the polyamide onto the sample and leave it to relax for 20 seconds. Remember to allow the polyamide to reach room temperature after removal from the freezer.
This is in order to maintain the filling properties over time. Spin the sample first at 500 RPM for five seconds with an acceleration of 100 RPMs to the negative one and ramp to 6, 000 RPM with an acceleration of 500 RPMs to the negative one for 60 seconds. Then bake the sample on a contact hot plate at 140 degrees Celsius for five minutes.
For a thicker polyamide film, spin multiple layers or reduce the final spin speed. Cure the polyamide on a contact hot plate at 220 degrees Celsius for 10 minutes. Next, deposit, 15%2010 PMMA onto the sample spin at 5, 000 RPM for 60 seconds.
Remove any excess resist that is crept onto the backside of the sample using acetone. Then bake in a convection oven at 180 degrees Celsius for 30 minutes. Once the sample has cooled to room temperature deposit 4%2041 PMMA onto the sample, spin and bake as shown earlier.
Now, design the job file in Tanner L.Edit fracture into polygons by layout Beamer. And finally, submit to the beam writer using the Java based bell software. Write the desired job using a dose of 450 micro curies centimeter squared on the VB six electron beam rider.
Next, develop the sample in a solution of one-to-one MIBK to IPA at 23 degrees Celsius for 60 seconds. Rinse in isopropanol. Then inspect for pattern fidelity on an optical microscope.
If features are poorly resolved, strip the resistant optical acetone and isopropanol and start again. Des scum the sample with oxygen using a gala, plasma prep barrel lasher then evaporate 20 nanometers of titanium and 150 nanometers of gold using an electron beam evaporator. Insert the sample into a beaker of warm acetone and heat to 50 degrees Celsius in a water bath for four hours using a pipette.
Wash the sample liberally with the warm acetone. Now inspect the sample by eye for metal lifting off from the areas where the PMMA was present. If the liftoff is progressing slowly, place the beaker in the ultrasonic water bath for two minutes.
Finally, inspect the sample under the optical microscope. Turn on the nitrogen supply to the Fourier, transform infrared spectrometer. Press the FIR button on the front of the spectrometer control unit to turn on the mercury arc lamp.
Insert the six micron multilayer beam splitter into the appropriate slot in the interferometer unit. Next, vent the sample compartment of the spectrometer and insert the pike 30 degree reflection unit. Place the seven millimeter aperture on top of the reflection unit aperture, and on top of this, put a gold mirror.
Now evacuate the sample compartment to a pressure of five millibar. Start the opus software and load the configuration file for taking measurements in the 30 to 300 inverse centimeters range. And sure the LED on the front of the detector compartment is flashing green indicating that the scanner is operating.
Check that the shape of the interferogram is as expected. Run 100 background scans to obtain the background spectrum. Vent the sample compartment, remove the mirror and place the sample face down onto the aperture.
Ensure the center of the sample is in the middle of the aperture, and then evacuate the sample compartment. Next, run 1000 sample scans to obtain the sample spectrum. The software automatically compares the sample spectrum with the background and the true reflection spectrum of the sample is displayed on the screen.
These figures show absorption spectra for metamaterial absorbers with differing dielectric spacer thicknesses. The 7.5 micron thick polyamide sample with no electric ring resonator structure has a maximum absorption of 5%across the frequency range of interest. The experimental data shows a resonance peak at 2.12 terahertz of 77%absorption magnitude.
This result is in excellent agreement with the simulated absorption maximum of 81%at 2.12 terahertz. Here, data are generated from MM absorbers with the same ERR geometry for different polyamide thicknesses ranging from one to 7.5 microns, and for an absorber where the dielectric is three microns of silicon dioxide. As the polyamide thickness increases from one micron to 3.1 microns, the peak absorption increases.
But at polyamide thicknesses greater than 3.1 microns, there is a slight reduction in the peak absorption value. A distinct red shift of 0.25 terahertz is observed as the polyamide thickness increases from one micron to 7.5 microns. The effective permittivity and permeability can be extracted from the simulated data via inversion of the S parameters as shown here for the simulated MM absorber with a 3.1 micron thick polyamide spacer.
The real parts of the optical Constance cross close to zero, A condition required for zero reflection at the frequency of maximum absorption. There is a peak of the imaginary component of the permeability implying high absorption.Erl. FDTD can also be used to establish the location of the absorption within the MM structure.
These plots clearly demonstrate that the majority of the energy is dissipated as omic loss in the ERR layer and as dielectric loss in the first 500 nanometers of polyamide. Below this layer, several applications such as terahertz spectroscopy require sensors that exhibit broadband terahertz absorption. We have developed two strategies to realize such broadband absorption.
The first strategy stacks alternating layers of metallic RR and dielectric layers on top of a continuous ground plane in different layers, crosses of differing lengths, support several resonant modes closely positioned together in the absorption spectrum. By tuning the dielectric thickness, the multi-layer structure can be impedance matched to free space at each resonant frequency and broadband absorption obtained. Then a standard electron beam registration process is used to align the RS on top of one another in a second.Strategy.
Four Rs incorporated into a four color super pixel are designed onto a single dielectric layer. Such a device is much simpler to fabricate than the multi-layer absorber. This plot shows absorption spectrum and simulated data for a multi-layer mm absorber of indicated dimensions.
The one layer structure has a single resonance peak at 5.42 terahertz, where 78%of the EM radiation is absorbed. In contrast, the three layer device has three closely positioned resonant peaks with a wide frequency band from 4.08 terahertz to 5.94 terahertz, where the absorption is greater than 60%To understand the origin of the spectral characteristics of the simulated absorption distributions in the XZ plane of the three resonances are plotted. These distributions clearly reveal that each ERR contributes to the broadband absorption Once mastered.
This technique can be done in less than four eight hours if performed Properly. While attempting this procedure is important to remember to be methodical and consistent when performing the fabrication steps. After watching this film, you'll have a very good overview of the micro nano fabrication technologies that we use that enable us to make a range of ertz devices and components including Metamaterial absorbers.
