The Postma Lab at CSUN

Nano Lab: The main laboratory, Eucalyptus hall 2023. On the left is the door into the cleanroom. We have feedthroughs from the cleanroom into the main laboratory, so we can control experiments running in the cleanroom with equipment located outside. To prevent damage to the ultra sensitive devices that we fabricate due to electro static discharge, the lab has dedicated humidity control keeping the humidity level at 60%. The floor has static dissipative tiling for the same reason.

DNA deposition: Saliha Akca at the pipet workstation preparing a DNA suspension for deposition on a wafer. The Eppendorf pipets allow for a reproducible deposition of a know volume from a few ul to a ml. This particular workbench has a view of the cleanroom and feedthroughs to connect to experiments running in the cleanroom. The 19" instrument rack on the right slides out and swivels to the side for access to the back of measurement instruments.

Electrical measurement setup: We measure electrical transport properties by contacting the device with gold-plated probes. Voltages are applied by the measurement computer and the current is amplified by the current amplifier. Several filter boxes allow for various types of signal conditioning, such as signal attenuation, (low and high-pass) filtering, and galvanic isolation. The measurement computer is used to visualize and analyze the acquired data.

Optical inspection: Jaime Osorio is inspecting a sample under the optical microscope in the lab. This optical inspection is the first inspection we do after we have performed electron-beam lithography on the sample. Afterwards, we image it with the AFM or SEM. The bench work surface is a grounded sheet of stainless steel with ground points in the front to connect wriststraps to. Cable gutters in the top allow for easy routing of cables from work station to work station all through the lab.

Ion current measurement: This setup is used to measure small ion currents through solid-state nanopores. A membrane containing a nanopore is immersed in salty water and a bias voltage is applied across the membrane. The ion current is analyzed as a function of the size of the nano pore, the surface charge, and thickness of the membrane. DNA is then introduced on one side and due to the negatively charged backbone, it translocates through the nanopore towards the positive chamber. The ion current is analyzed while the molecule translocates, revealing the time and speed of translocation, the shape of the molecule and the charge.

Henk Postma is going over the DNA deposition procedure. In the upper right corner is a diagram depicting proper flow balancing of the storage area under the wet processing stations in the cleanroom. Behind Henk is the door of the gowning area for the cleanroom. The pressure gauges on the right indicate the relative air pressure in the cleanroom as well as the gowning area. The cleanroom must be at higher pressure than the gowning area, which in its turn has to be at higher pressure than the main lab.

Class 1000 cleanroom: The hoods on the left are for wet organic and acid processing and are class 100. This is where devices are cleaned, electron-beam resist is applied, baked out, etc. A 'spinner' in the leftmost bench is used to evenly coat wafers with electron-beam resist. The blue workbenches on the middle are for sample inspection. An oven and oxygen plasma cleaner are installed on the furthest bench. The metal evaporator is on the right.

Metal Evaporator: The metal evaporator is used for deposition of thin films of metal on wafers. A wafer is mounted in the vacuum bell jar (on the top). A tungsten boat is loaded with the material that we want to evaporate. The bell jar is closed and evacuated down to a pressure of about 5e-7 mbar. A high current is then applied to the tungsten boat, heating it up, and the metal starts to melt and slowly evaporate, thereby covering the wafer with metal. The evaporation rate is monitored with a chrystal thickness monitor. Evaporated metal increases the effective mass of the crystal and consequently lowers the resonance frequency. By tracking the frequency, the amount of evaporated material is measured. Typical materials we evaporate are gold, palladium, and chrome and we usually evaporate about 50 nm thick layers.

Mike Dickson and Yogeshwari Patel are mixing chemicals at a workstation in the cleanroom. The body suits are worn to prevent dust coming off clothes and contaminating the room and/or samples.

Mike Dickson and Yogeshwari Patel are cleaning a Silicon wafer in the class 100 chemical hoods in the cleanroom. The air in these hoods is cleaner than the air in the cleanroom so air flow is balanced to prevent air from going into the hoods while at the same time preventing volatile gasses from the hoods spilling out of the hood back into the room.