http://www.njit.edu/old/mfc/
121 Summit Street, Room 200, Newark, NJ 07102
Tel. 973-596-5696; Fax. 973-596-6495; e-mail: ivanov@njit.edu
Cleanroom
The IR filter prototypes are fabricated in the Class-10 cleanroom lab of the
Microelectronics Fabrication Center at NJIT. The lab is equipped with microfabrication
MEMS technology including 1 micron resolution contact photolithography, wet chemical etching, reactive ion etching (RIE), deep reactive ion etching (DRIE), magnetron sputtering, e-beam evaporation, wafer bonding, plasma-enhanced chemical vapor deposition (PECVD), low-pressure chemical vapor deposition
(LPCVD), wirebonding, ellipsometry, profilemeter microscope, optical microscopes, and electrical test equipment. The MFC serves as an interface between industry and academia. The Center provides R & D and foundry services to companies, trains students and engineers, and runs research projects in the field of BioMEMS, integrated circuit fabrication, integrated optical devices, chemical and gas sensors, pressure sensors, and biometrics micro-electro-mechanical systems (MEMS). MFC specializes in fast prototyping of innovative microsystems using silicon, glass, polymer, piezoelectric, and ferroelectric wafers. Current techniques used in the
MEMS technology are: dry and wet oxidation, chemical vapor deposition of silicon dioxide, silicon nitride, polysilicon, amorphous silicon, fusion wafer bonding, anodic wafer bonding, thermocompression, high aspect ration wet and dry etching of silicon and glass, thick positive and negative photoresist patterning.
The cleanroom staff comprises a Process Development Engineer, Dr. Rajendra
Jarwal, Facility Engineer, Mr. Lev Markov, and Lab Manager, Dr. Dentcho Ivanov.
Description of Filters:
Inductive metal meshes are two dimensional periodic metal structures with periodicity constant g and openings of various geometries. There is diffraction for wavelength smaller than g and resonance transmission for peak wavelength longer than g, used for band pass filters. The inverse structure, a periodic structure with metal islands on a substrate, is called a capacitive mesh and used for blocking filters.
Resent use of computer simulation programs has largely enhanced the knowledge of the relation of peak wavelength of the resonance to periodicity constant, size and shape of the openings, thickness, substrate thickness and refractive index.
Filter Types to be manufactured:
Inductive metal mesh filters, thin on a plastic substrate and thick, free standing or with substrate.
Capacitive metal meshes, thin and thick on a substrate.
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Required Specifications for the Production of the Filter:
Periodicity constant
Size and shape of opening
Thickness and metal
Area of the mesh
Substrate material and refractive index.
Simulation Methods and Agreement with Experimental Results.
The simulations have been performed using the Micro-Stripes program and
Transmission Line Theory. The peak wavelength of the filters, calculated with simulations, have been compared with samples, made very accurately with X-ray lithography. The agreement with resonance peak wavelength is within 3% when using a conductivity value obtained by matches the intensity of the calculations with the experimental data. In the following publications are some of the published simulations and comparison with experimental samples.
Publications on Metal meshes and Filters.
“Far-Infrared Transmission Filters for the 300-18 cm-1 Spectral region”, by
K.D.Möller, D.J.McMahon, and D.R.Smith, Appl. Opt. 5, 403 (1966).
“Far-Infrared Bandpass Filters and Measurements on a Reciprocal Grid”, by
G.M.Ressler and K.D.Möller, Appl. Opt. 6, 893 (1967).
“Far-Infrared Interference Filters”, by S.P.Varma and K.D.Möller, Appl. Opt. 8, 1663
(1969).
“Far-Infrared Filters made from Inductive and Capacitive Cross Grids”, by
V.P.Tomaselli, D.C. Edewaard, P.Gillan, and K.D.Möller, Appl.Opt.20, 1361 (1981).
“Cross-shaped bandpass filters for the near- and mid-infrared wavelength regions”, by K.D.Möller, J.Warren, J.B.Heaney, and C.Kotecki, Appl.Opt.35, 6210 (1996).
“Thin and thick cross shaped metal grids”, by K.D.Möller, K.R Farmer, D.V. P.
Ivanov, O.Sternberg, K.P.Stewart, P.Lalanne, Infrared Phys. 40, 475 (1999).
“Near Field Effects in Multi-layer Inductive Metal Meshe”, by K.D.Möller,
O.Sternberg, H.Grebel and Kenneth P.Stewart, Appl.Opt.41, 1942-1948 (2002).
“Inductive Cross shaped Metal Meshes and Dielectrics”, by K.D.Möller, O.Sternberg,
H.Grebel and Kenneth P.Stewart, Appl.Opt.41, 3919-3926 (2002).
“Thick inductive cross shaped metal meshes”, by K.D.Möller, O.Sternberg, H.Grebel and Philippe Lalanne, Appl.Phys.91, 9461-9465 (2002).
“Inductive Cross Shaped Metal meshes on Silicon Substrate”, by O Sternberg,
K.D.Möller, H.Grebel, K.P.Stewart
44,17-25 (2003). and R.M.Henry, Infrared Phys. and Technology,
“Thick capacitive meshes on polyimide substrate”, by A.Lüker, O.Sternberg, H. Hein,
J.Schulz and K.D.Möller. Infrared Phys. and Technology, 44, 153-157 (2004).
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Examples of Simulations:
1. Filters with Bandwidth of 10% and 80% Transmittance.
The metal mesh filters should have a required peak wavelength and 10% bandwidth and 80% transmittance. Simulations using meshes with circular openings have shown in the long wavelength region results. In Fig.1 are shown the transmittance of metal foils of normalized thickness tn = 0.43g and normalized hole diameter dn =
0.68g, in a rectangular arrangement of periodicity g.
1
0.8
0.6
0.4
0.2
0
1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Normalized Wavelength
Fig.1. Simulated transmittance over normalized wavelength λ/g of a filter of 10% band width with circular openings in a rectangular array of thicknesses t=0.43g and opening diameters d=0.68g
2. Fine Tuning using Dielectric Layers.
The attachment of either a thin layer of specific thickness to a metal mesh, or two layers of different thicknesses and refractive indices, has a shift of peak effect on the resonance wavelength. The amount of shifting is shown in Fig.2 and depends on the thickness of the
Gap: 0.5
1.00
Gap: 1
Gap: 2
0.80
Gap: 0
Gap:3
0.60
0.40
0.20
0.00
20 30 40 50 60 70 80 90
Wavelength in µm
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Fig. 2. Shift of resonance wavelength as a function of the position at various gap distances of 0, 0.5, 1, 2, 3μm from an inductive screen. The dielectric is made of
0.5μm Silicon. At gap = .5μm, a resonance shift of 18% with respect to the “no gap” position, is obtained. slab as well as on the refractive indices of the layers. When placing a thin dielectric film close to the mesh, but not attached to it, the resonance wavelength shifts to shorter wavelength depending on the distance (gap) between the film and the mesh.
By proper manipulations of the thin film in the near-field region, the desired filter response may be obtained
3. Broad Bandpass Filters
Simulations of a filter made of several loop shaped inductive meshes shows a broad bandpass, and is tunable over a certain spectral range by changing the separation between the meshes. It is called a coax-filter in analogy to a coaxial cable which transmits large ranges of frequencies.
Transmission line theory has been used for the calculation of the transmittance, see
Fig.3 of four coax-meshes at separations of 3, 4, 5, 6, and 7μm. These transmission line calculations are confirmed by Micro-Stripes calculations.
Separation in microns
1
0.8
0.6
7
3
0.4
0.2
0
0 10 20 30 40
Wavelength in m m
50 60
(a) (b)
Fig.3. a. Transmission line calculations of coax filters of four layers at separations between
3μm and 7μm. b. Coax pattern as a combination of an inductive and a capacitive mesh.
4. Medium size band pass filter.
A simulation for such a filter is shown in Fig.4. The filter should have less than 1% transmission at 19µm, then rise to at least 70% at 23µm, and continue to have about 70% transmission to 27µm. The width of band should be 20%. The simulation shown in Fig.4 assumes four cross shaped meshes with periodicity constant g =
17µm, cross separtion 2a= 1.45µm, width of cross arms 2b=2.6µm and thickness
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t=3µm. The meshes are lined up with their openings and the thickness of the spacers s=5.5µm.
1
0.8
0.6
0.4
0.2
0
18 22 26 30 34 38 42 46 50
Fig.4. Simulated transmittance of four cross shaped meshes with g = 17µm, cross separtion of 2a=1.45µm, width of cross arms 2b=2.6µm and thickness t=3µm. The meshes are lined up with their openings and the spacers have thickness s=5.5µm.
5. Broad Band Stop filters.
Broad band blocking filters using 8 capacitive meshes were produced by K.D.Möller and flown by P. Richards in his Balloon experiment to study Comic Background radiation.
Simulations using Micro-Stripes have shown that the blocking region of capacitive meshes of metal loops are larger than with squares. In Fig.5 we show two mesh filters made of square shaped and loop shaped meshes. The spacing is ½ of the resonance wavelength, determined from the peak blocking area of one mesh. The two loop mesh shows a broader blocking region and higher transmittance in the long wavelength region.
1
0.8
0.6
0.4
0.2
0
1 3 5 7
Wavelength/Periodicity Constant [λ/g]
9

R
/2
(a) (b)
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Fig.5. a. Comparison of transmittance of a two capacitive square mesh filter with a two capacitive loop mesh filter. b. Schematic mount of two mesh filter.
6. Broad Band Blocking Filter.
In Fig.6 we have plotted the transmittance of four loop mesh filters with periodicity constants 40, 80, 160 and 320µm and the same ration of the loop parameters to the periodicity constant ( outside ration: 34/40, inside ratio: 14/40).
Capacitive Loops on Polyethylene
1.00
40
0.80
80 160 320
0.60
0.40
0.20
0.00
Wavelength [ m m]
Fig.6. Blocking of spectral region from 40 to 900µm using 4 filters, each with blocking of one octave.
Powder Filters:
We are developing a cleanroom method to produce Yoshinaga powder fillers for the
. blocking of short wavelength radiation in conjunction with Broad Band Blocking
Filter.
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