{"id":17,"date":"2018-05-24T16:37:37","date_gmt":"2018-05-24T16:37:37","guid":{"rendered":"https:\/\/physlabs.colostate.edu\/lithography\/?page_id=17"},"modified":"2020-05-22T22:00:17","modified_gmt":"2020-05-22T22:00:17","slug":"research","status":"publish","type":"page","link":"https:\/\/physlabs.colostate.edu\/lithography\/research\/","title":{"rendered":"Research"},"content":{"rendered":"
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An array of gold electrical contacts patterned on a silicon wafer. Each die is 6 x 6 mm.<\/figcaption><\/figure>\n

One of the primary uses of the LW405C is defining microcircuit geometries.\u00a0 The image to the right shows an array of four gold contact sets patterned on a scribed silicon wafer.\u00a0 This array was patterned in about 10 minutes on the laser writer and then coated with gold.\u00a0 Once broken apart, each\u00a0die<\/em> will be covered with photoresist and patterned with the laser writer again, exposing a microbridge geometry across the ends of the gold pads.\u00a0\u00a0\u00a0The dies will then be sputter coated with granular aluminum oxide and cleaned, leaving metal only where the microbridge pattern was exposed.\u00a0 The edges of the deposited bridge are etched away in another lithographic step followed by broad-beam argon ion milling.\u00a0 The image below shows a completed microbridge.\u00a0 The dark background is the silicon nitride wafer surface.\u00a0 The two gold leads at the bottom of the image will be used to measure a voltage difference as current flows along the sample.\u00a0 The light colored sample is granular aluminum oxide.<\/p>\n

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A 50 \u00b5m-wide, 200 \u00b5m-long granular aluminum oxide microbridge. The gray regions above and below the bridge are areas where the surface nitride of the wafer has been etched away.<\/figcaption><\/figure>\n

This particular film has a superconducting transition temperature of 1.609 K, below which the electrical resistance of the material goes to zero and small magnetic fields are expelled from the bridge.\u00a0\u00a0For higher magnetic fields,\u00a0 quantized filaments\u00a0of magnetic flux force their way into the bridge.\u00a0 These\u00a0vortices<\/em> produce a magnet field above the bridge surface that can be measured by a magnetic probe.<\/p>\n

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Magnetic flux vortices in superconducting granular aluminum oxide image by scanning Hall probe microscopy. \u00a9A.D.DeMann 2018<\/figcaption><\/figure>\n

By scanning a small Hall probe just above the bridge, the out-of-plane component of the magnetic field can be measured.\u00a0 The image to the right shows a magnetic micrograph of the middle of the granular aluminum oxide bridge at 1.450 K in a 1.5 G field.\u00a0 The bridge edges are clearly visible because the currents flowing produce relatively large magnetic fields.<\/p>\n

–<\/span><\/p>\n

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An aluminum superconducting nanowire fabricated by Weston Maughan.<\/figcaption><\/figure>\n

Weston Maughan, a graduate student in physics, used the LW405C to create a superconducting nanowire.\u00a0 The wire will be cooled to ~1 K and scanned with a cryogenic atomic force microscope to investigate the phenomena of phase slips in low-dimension superconductors.\u00a0 The fabrication process requires at least six lithographic exposure steps, each of which much be carefully aligned.\u00a0 The upper portion of the image shows a binary de Bruijn sequence etched into the silicon wafer which is used to determine the position of probe relative to the wire.\u00a0 The gold contacts to the left and right lie along a step etched into the silicon.\u00a0 By depositing superconducting material normal to the substrate surface and then ion milling the material away at an angle, a small filament of material is left in the shadow of the step.<\/p>\n

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A thin magnetic layer on a sapphire substrate fabricated by Jinjun Ding.<\/figcaption><\/figure>\n

The bridge geometry shown to the left is used extensively to probe material properties such as resistance, carrier mobility and density, and the Hall coefficient.\u00a0 This particular geometry was designed and created by Jinjun Ding of Dr. Mingzhong Wu’s group in the Department of Physics at CSU.\u00a0 The magnetic film was deposited on the sapphire substrate.\u00a0 Photoresist was spun on the film surface and selectively exposed with the LW405C.\u00a0 Once developed, the photoresist only covered the portions of the magnetic film which remain in the image.\u00a0 A broad beam argon ion mill was used to remove the film in the areas not protected by resist.\u00a0 \"\"Finally, the resist was removed with acetone leaving the structure shown.\u00a0 This bar will eventually be tested with the physical properties measurement system (PPMS) in the CIF at CSU.<\/p>\n

Jinjun Ding also fabricated a Hall bar using the laser lithography facility, shown in the image to the left. This particular Sn\/CoFeB bilayer Hall bar has a ~5 \u03bcm gap (dark stripe) between the contacts (light grey) and was used to study spin-orbit torque-induced magnetization within this material.<\/p>\n

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Biosensor electrodes fabricated by Jasmine Najed.<\/figcaption><\/figure>\n

Jasmine Najed, a graduate student working in Dr. Tom Chen’s group, used the laser lithography system to fabricate biosensor electrodes with a liftoff process. The electrodes were patterned in s1813 photoresist and then developed and metalized.<\/p>\n

\n","protected":false},"excerpt":{"rendered":"

One of the primary uses of the LW405C is defining microcircuit geometries.\u00a0 The image to the right shows an array of four gold contact sets patterned on a scribed silicon … <\/p>\n

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