Exam questions of today (2015.08.06):Full course name: "362.118 Mikroelektronische Konzepte für Biomedizinische Interfaces / Microelectronic Concepts for Biomedical Interfacing (Wanzenböck/Bertagnolli, 2014)"
1) negative photoresist.
A: One of the two kinds of photoresist (pos/neg). It´s the one that gets crosslinked when exposed to light. Therefore the parts of the negative resist exposed to light will remain when the resist will be washed of after the exposure process. It creates a negative mask and therefore it´s called negative photoresist. A pos. PR. would get weaker when exposed to light and will be washed away.
1a) Where do you use the resist? What for?
A: As a protection layer for the etching or lift-off process. Parts of the material not covered by the resist will be edged away. Or in Lift-off, the whole surface is coated, but when the resist get´s removed (=lift-off), only the surfaces where there was no PR. remain coated. Generally you use a resist to apply the masks structure to a surface for thin, structured layer creation
A: CVD stands for chemical vapor deosition. A heated wafer surface is floated with a substance that is brought in the gasous phase by attaching speciall residuals. The substance (called primer) adherse to the surface, reacts on the surface and when the surfae is heated correctly, the residuals fly o again.
2a) What other deposition methods do you know? Which one we used in the lab?
There are physical and chemical deposition methods. Beside chemical vapor, also a cehmical liquid deposition is used to create galvanic elements. Both would lead to a total surface coverage of the desired substance. If you only want a top level coverage, but nothing on the sides, you are better off with physical techniques.
There is physical vapor deposition, the kicking off ions by electrons and the plasma methode we used in the lab to have solid particles (gold in our case) being brought into plasma state to cover the surface.
3) Passage number
A: Passage # is the # of times a cell culture has been subcultured. Starting from a primary culture, the culture grows and at some point has not enough nutrietients, oxygen and other important incredients anymore. Therefore it must be subcultured. How do we realize this in the lab? In the lab we used the enzyme trispin to cut the glycoproteins that link the cells together. Sources for cells are eggs, embyos or tissue. Then a small amount is taken from the host by biopsy. Enzymes like tripsin cut this cell network into single cells that can grow, adhere and form cell layers. Can you let the trispin in there all the time? No, one has to remove the tripsin after certain time, otherwise the tripysin "eats" away the cell membrane and destroys the cell. Removal is done by centrifugation, since the medium with the tripsin has lower density then the cells. The medium with tripsin get´s removed (->pipette) and fresh medium will be added to the cell culture. Now the cells can grow there..
4) Reynolds number: flow pattern, why turbulent flow, key parameters?
A: Depends on the viscosity, speed of the fluid and diameter of the tube. Low Re -> laminar flow, high Re-> turbulent flow. Turbulent flow is used in case we want to mix substances, as in the case of LAMINAR flow there is NO MIXING. Two inlets of liquid into a tube with laminar flow patterns of those liquids would form seperated layers, where the layer thickness only depends on the input flow rate. Laminar flow patterns are parabolic, whereas turbulence leads to the creation of eddies that encourage the mixing process.
5) metall/ electrolyte interface. Draw and explain
A: Helmholtz layer creation at the interface. See
Biomedical Signals and Sensors I (Kanasius)
6) neuron FET. Draw it, draw FET, whats the difference?
A: Drawing like IsFET, just with neuron on top of gate. Explained the reference electrode, since we again have a metall/ electrolyte interface. IsFet in all cases of ionic current translation to electrical current.How is the signal processing happeningIf the neuron would perfectly attach to the semiconductor we would have an compact dielectric which is coverned by electronical polarisation. This is not the case for neuronFETs! Cell adhesion is coverned by proteins. Those proteins keep the lipid CORE of the membrane a certain distance away from the semiconductor. This distance is known as the cleft, filled with electrolyte and several nm thick (measured by interference). We don´t have direct contact anymore and need a "transductive electronical potential" either created displacement currents of the membrane as result of neuron activiety, or by displacement current alongside the wave due to a voltage applied to silicon. If you want to model it you use the model of the core-coat conductor and either the two-dim area- contact model or the zero-dim point contact model to descirbe current and voltage in the gap.
More on question 5 can be found in the attached document called "Neuroelectronic Interfacing"
Attached you will also find a short summary to this course. It is not comlete. I´ll try to give it a second shot when I´ll find the time.
Please feel free to change the document, correct it, transform it- make it a better study-resource for your fellow students!
All the best with your studies,
ps.: All lecture slides attached. Please be aware that they contain personal comments (lecture notes) made with pdf-Xchange.