FMN Laboratory team participated in MNE 2018

20 september 2018

In recent ten years a lot of researches in plasmonic sensorics are made. Different types of plasmonic devices can be used in wide range of application: nanoscale coherent light source, different gas, biological, liquid, magnetic sensors, transmission lines and etc. This is due to the inherently high surface sensitivity of SPR structures which can produce strong changes in optical intensity in response to analyte interacting with surface chemistry. 

Basic rules of fabrication high quality plasmonic device is the metal film with specified parameters and high precise structuring. We demonstrate investigation and research in both sides of plasmonic device fabrication. By far fabrication is serious problem for the plasmonic devices. Losses in metals is one of the main plasmonic problems. To solve it, it is necessary to pay serious attention to the choice of the plasmonic material: its deposition methods and the deposition regimes for obtaining optimal properties. We use silver and gold films for plasmonic application. Theoretically silver layer have largest plasmon propagation length but gold is more stable layer in fabrication process and compatible with biological applications. Of course, propagation and losses depends of crystalline structure of the film. Ideally way is to use the single-crystalline structure of the silver film. That can give best properties of plasmonic device. We obtain this type of film at silicon substrates with super low roughness of surface. Nevertheless, on transparent substrates like glass and sapphire it is not possible to form this type of film. In our work, we demonstrate different types of film with different application for different devices.

As usually to fabricate plasmonic device focused ion beam milling is used. But it is well known that main problem of this technique is extremely low processing speed. For this reason in our work, we use e-beam writing at high speeds and dry etch of films trough formed mask. Also inorganic resist HSQ can be used like optical part of plasmonic sensor. It allows us patterning array of big structures up to 500x500um each in acceptable time. In case when plasmonic device fabricated on quartz substrate before metal deposition it cause charge problems during e-beam patterning. Accumulated charge dramatically changes shape of patterned structures. To avoid using additional metal films we using spincoated polymer films to dissolve surface charge and screen hidden charge in substrate. Hidden charge cause significant decrease of patterning contrast because of rising backscattering. To solve this problem we using changing of development parameters increase back contrast of patterning image. At fabrication, we pay attention to increase quality of fabricated structures: studying roughness of lines, reproduction of elements, deviation of pitch inside the periodic structures, widening of process window, increasing of resist contrast of patterning.

Thus, we can fabricate high quality plasmonic sensors that can be reproductively produced for many different applications. All our investigations allow achieving high senility. 

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