Boston Aluminum Oxide as High Index Material for Optical Coatings Presentation

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Background Information:

The independent case study projects will be used to investigate the numerous and varied applications of bulk, thin film and nanoscale materials in electronics and photonics. The class will be divided into teams consisting of two students (sometimes 3 due to class size). Each team will select a material, or class of materials as the focus of their case study project. There are two parts of the case study. In a series of in-class presentations, students will fist discuss the application or potential application for the material, the desired material properties for the application, and the candidate synthesis methods that can be used to fabricate the material as outlined in there abstract. In the second part, the should select and discuss the synthesis or fabrication method which they believe will yield the best results for their particular application as outlined in there abstract.

The in-class presentations are intended to provide a forum for students to develop their oral communication skills. Consequently, style, organization and delivery will constitute a significant portion of the grade for the presentation. Software such as Power Point should be used to prepare overheads for the presentations. Figures, graphs, schematics and illustrations should be used as much as possible in the body of the presentation. References should be embedded in the slides, as appropriate. It is also important to make sure that the presentation does not extend beyond the allotted time with questions. As a rule of thumb, students should prepare 3-4 overheads for 5-minute talks. The presentations will be graded 75% on style (clarity of presentation and view graphs, organization, delivery) and 25% on technical content (technical accuracy of presentation and discussion, originality). The style portion will be graded by your peers (the average of the scores) and the instructor will grade the technical content. Written comments from students and the instructor will serve as feedback on your presentations.

A schedule for presentations will be worked out early in the course. Students may informally trade time slots but must inform the instructor in advance of the schedule change. Failure to give a presentation at the scheduled time will result in a zero for the presentation.

Summary

Students will be divided into pairs and each pair will select a topic for the case study project. There will be two presentations over the course of the semester covering different aspects of your case study/design project as outlined below:

Part I: Presentation on applications and desired properties of material.

Part II: Presentation on potential best synthesis techniques.

I have done part 1 and I want you to continue writing E-beam evaporation and ion beam sputtering’s advantages and disadvantages. Let me attached the scripts and power point I have done for part 1.

script

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Our case study is on aluminum oxide as the high index material for optical coatings and exome or laser photolithography. My name is gunner Scott and I will be talking about applications and desired material properties and that candidate synthesis methods. And then Alice will present on the best synthesis method for our application. Lithography is the process in which light transfers a geometric pattern from a photo mask or radical onto a chemical photoresist which is on its substrate. The pattern can then be etched into the substrate with a series of chemical treatments before finally stripping off the remaining photoresist from the patterned substrate. The mask is typically made of some sort of glass such as SIO2 With the chromium layer to give you the pattern on the photoresist is typically some sort of hydrocarbon. We’re specifically going to be looking at exome or laser photolithography. X-ray lasers are lasers in the ultraviolet that typically come from a combination of a noble gas, such as argon or krypton in a reactive gas such as fluoride. Many of the dominant technologies for the manufacture of integrated circuits make use of this class of lasers, with the primary ones being argon fluoride at a 193 nanometers, and krypton fluoride at 248 nanometers. There is a direct relationship between the size of the feature you can achieve on a chip and the wavelength, wavelength of light being used to expose the photoresist. You can see in this equation that as you decrease your wavelength lambda, you also decrease the minimum feature size W. Another way to get smaller features is to decrease your numerical aperture NA, which describes the focusing strength of the projection system. The issue with this is you run into competing variables because another factor that determines the feature size you can create is the depth of focus. Depth of Focus gives a range in which the light is in focus on the wafer. And if the depth of focus is larger than the variation in surface height, you will not be able to generate accurate features. As you can see from the depth of focus equation, if we increase the numerical aperture by too much to decrease the minimum feature size than we’re also decreasing with depth of focus, potentially to a point where it won’t work. High-performance optical coatings are essential and photolithography, you can see from the picture on the right that it deep UV photolithography machine has a system of coded mirrors and lenses that are responsible for directing and shaping the beam prior to reaching the mask. You can also see in this picture on the far right, how the light reaches the radical before going through a focusing lens, which will then focus that pattern down to a smaller size onto the wafer. And the wafer is usually on some sort of stepper that will move it back and forth. Pattern this image along the wafer. The first property of interest to us is high reflectance at the desired UV wavelengths. If you think about having a series of, say, ten mirrors in a system with 70% reflectance at each mirror, then you can see how rapidly you lose your signal and you would only have 70% of your incoming signal bounce off of the first mirror and then 49% off of the second mirror and so on and so forth. So therefore, it is very important to have something on the order of high nineties for reflection percent, which is shown in the image on the right. You can see that this mirror has probably over 97% reflection at a 193 nanometers. On. Many of the other high index materials that are often used in optical coating applications are not very effective in the deep UV region due to the extremely large extinction coefficients they have. Two of the other common high index materials are ten alum pentoxide and hafnium dioxide. But the problem with those is tan alum begins to absorb almost everything below 300 nanometers, while hafnium usually absorbs everything below about 250 nanometers. Aluminum dioxide, on the other hand, has a K_a value on the order of ten to the minus three in this range, which makes it an ideal candidate for DPV applications. Next property we’re going to discuss is lasered Amos threshold. Laser damage threshold is a measure of the amount of laser damage and optical component can withstand before it begins to fail. Which is very important because these machines are incredibly expensive. So the last thing that you would want is to have the optical components in the system fail faster than they should. One parameter that has shown a correlation to highlight or damaged threshold is the energy band gap, which you can see in this curve on the left. How as you increase the energy band gap, you also increase your ability to resist laser damage. And aluminum oxide has a pretty high energy band gap. It’s right around seven electron volts. When it comes to the laser damaged threshold there multiple factors to consider when discussing the mechanisms of laser induced damage. And based on these different factors, you will see different types of failures for different reasons. The most important factors that we need to consider, our laser wavelength, laser repetition rate, influence, which is the energy delivered per unit area. And because of how many possible combinations there are and how you would see different damage with a CO2 laser at 10.6 microns, for example, vs exome or laser that cause different types of damage for different reasons. And there are just too many to focus on. So we are going with the high fluence, low repetition rate exome or lasers. And for these, the primary damage mechanism comes in the form of microscopic voids in the coding. And basically as you repeatedly expose these coatings to high-energy laser pulses, these voids will begin to grow is you can see in this image on the right, the image on the left is pre, onset of any sort of damage. And then you can see that it it begins to rapidly grow these massive defects and pinholes. So for the candidate deposition methods, we found that there are many ways to deposit aluminum oxide. Them the biggest ones that we saw were electron beam evaporation, ion beam sputtering, atomic layer deposition and chemical vapor deposition. We we found that E-beam evaporation and ion beam sputtering seem to be the most relevant technologies for use with multi-layer optical coatings. Whereas atomic layer deposition and chemical vapor deposition seemed to have entirely different applications. So the two that we are going to be looking into the most will probably be E-beam evaporation and ion beam sputtering.