Reflections
EE 541 - Solid-State Sensors
The Solid-State Sensors course was about electronic sensors, their working, and applications. This course was one of my favorite courses. Electronic sensors get utilized in various applications ranging from simple temperature sensing to fully automated systems. EE 541 was a complete package to understand the manufacturing of sensors and their applications for different solid-state sensors, including acoustic, mechanical, electrical, magnetic, radiation, thermal, chemical, and biological sensors. This course was about understanding how sensors get fabricated and their operating principles.
Solid state sensors provided in-depth exposure to a current solid-state sensor device development. During this course, I identified a topic, conducted an information search through recent journals and publications, collected and organized the information on that topic, and prepared a technical paper presenting the information gathered. The topic I identified was Passive infrared Sensor.
Everything emits some low-level radiation. The hotter the material is, the more radiation it emits. A passive infrared sensor (PIR) means it does not generate energy but can store or dissipate energy. Infrared is electromagnetic radiation that is not visible to the human eye. The PIR sensor has pyroelectric materials which detect thermal energy. This word pyro comes from Greek which means fire. The pyroelectric materials are similar to piezoelectric materials. In piezoelectric materials, the displacement is converted into a voltage, whereas in pyroelectric materials, the temperature change does so.
Some PIR sensors available in the market come with an onboard processing unit. The onboard processing unit converts an analog signal into a digital signal. There are controlling units for changing the sensitivity of the sensor. This sensor has the same three pins of power supply, ground, and output. In addition, there are two potentiometers to control the working distance span of the sensor and the time delay of the sensor. There are two connections for selecting the mode of operation. The mode of operation is either the single trigger mode or the repeat trigger mode.
When there is a movement in front of the sensor, the split pyroelectric elements detect the temperature change. These two parts of pyroelectric materials are connected if there is no movement, they can cancel each other. If one part detects more or less IR radiation than the other, the output changes accordingly. These signals from the pyroelectric materials are amplified and then given to the comparator circuit, a lens for increasing the range of the sensor.
The PIR sensor with an onboard processor converts the analog signal to a digital signal. The onboard processing unit provides two potentiometers. One is to control the time delay for some time of whatever function like light on/off or security and alarm notification. The second potentiometer is to adjust the range for the sensors. Along with these, the sensor also provides two different modes of operation. The first one is single triggering and the second one is repeated triggering.
In this single triggering mode, when there is a motion, the sensor is triggered and waits for the set time delay before the next trigger. After the first motion detection and the second trigger occurs before completing the time delay, it will not get triggered. Only after completing the first time delay, the next trigger takes place.
In the repeat triggering mode, when there is motion, the circuit is triggered. If another movement happens in the targeted area, whichever the process was going on, it continues from that trigger for the set time delay. This process continues until there is a movement in the set delay.
The PIR sensor has a much different application. As a motion detector, the PIR sensor is present in automatic lights, security, and alarm systems. Other applications are automatic recording cameras, automatic doors in offices, and malls, scaring props on Halloween, etc.
The size of the sensor is small, and it requires very little power to work. So, this sensor is suitable for indoor and outdoor applications (solar-powered applications can work using a PIR sensor). With an onboard processor, the sensor provides more features, such as controlling the sensitivity and mode of operation. There are many uses of the PIR sensor in automation systems, security, and alarm systems, etc. The use of the PIR sensor is simple and effective in many applications. In the future, the use of this sensor and its appliances will increase as technology advances. This course was the best way to visualize the course’s theoretical and practical outcomes.
After taking this course, I understood working principles and application of solid-state sensors. After knowing how semiconductors devices got manufactured and processed, the manufacturing industry fascinates me. Semiconductors are the main ingredient in every electronic type of equipment. I will recommend this course to other electrical engineering students. I would do this course again because there is no shortage of sensors available to learn and use. It was a great learning experience. If students want to work in solid state field, this course will benefit them, and it looks good on their CV.
EE 559 - Semiconductor Device Physics
In the Semiconductor device physics course, I learned about the introductory physics of semiconductor materials. This course benefited me by covering /teaching the fundamentals and operation of electrical devices. This course gave me a new foundation for my future endeavors. It helped me build a strong foundation for semiconductor industrial jobs. Introduction to silicon-based devices for logic electronics, MOSFET device operation, the Band structure of materials, P-N junctions and diodes, Photovoltaic devices, contact resistance, and Phonon transport, examples of novel low dimensional materials for electronics and optoelectronics are a few topics covered in the course. These topics are intriguing to me and got me excited.
Semiconductor device physics gives me a good overview of the atomic scale working in semiconductor materials. Also, this course helped me improve my theoretical knowledge. I was not much into the theory, but after this course, I realized how important it is in the semiconductor industry.
The major problem I faced was theoretical concepts have no visual presentations. It is difficult trying to understand their behavior. For example, Professor assigned different theoretical concepts to students and for me it was the Schottky diode its works and its importance. The challenge was to give a presentation on an unfamiliar topic for more than 20 minutes. I learned how the Schottky diode works and its importance. As a result, I gave a presentation for about 30 minutes to my classmates. The course was a little frightening at the start, but later, I tried to understand the concept, and with some help from the professor I conquered my fear of theoretical knowledge.
Almost every electronic component has semiconductor materials. These components connect to the metals for a particular device to operate. So, the connection between metals and semiconductor is crucial.
When there is a junction between metal and semiconductor, it can be one of the two types.
The junction at which the workfunction of metal (Fm) is greater than the workfunction of semiconductor (Fsc) is known as the Schottky junction. The most important rule, when there is a junction, the fermi level must line up at equilibrium. Considering a metal with EF as its Fermi level and workfunction Fm, also a semiconductor with workfunction Fsc, its ECB is its conduction band energy, EF is its Fermi level, and EV is its valence band energy.
The emission of charged particles from the surface of heated material is known as Thermionic emission. The charged particles are the electrons. This process is not the only case for thermionic emission. When the electrons travel over the barrier, the process is known as Thermionic Emission. In this case, the junction is forward biased, and the electrons travel from the semiconductor to the metal over the Schottky barrier.
The other type is the ohmic junction where the value of Fm is less than the one of Fsc. As the energy bands of semiconductors are higher than the metal’s energy band, there is no barrier to oppose the electron flow. Therefore, in forward and reverse biased conditions, the electrons can travel freely with some resistance as shown in figure 3.
The Schottky junction works as a rectifying circuit. It is better than the normal P-N junction considering the less voltage drop in forwarding biasing condition and breakdown point in reversed bias condition. The Ohmic junction acts as just resistance in the circuit. The current flow in the Schottky and the ohmic junction is by majority carriers instead of minority carriers in the P-N junction. In the Schottky junction, the electron flow is by the majority thermionic emission, and some by tunneling.
These concepts are crucially important in every electronic device. This course was more of a steppingstone in the field of semiconductors. Here, I learned new concepts, tried new approaches to semiconductor material that are theoretical based. I improved my presentation skills, and I got the courage to wander into a new field of study. The final presentation was an opportunity to demonstrate my strength in this field. Also, to prepare and talk about an unfamiliar theory. At the conclusion, the professor was also impressed with the data I presented, and the presentation was easy enough to understand by other students.
I would recommend to others that they take this course because it can help them understand the working of semiconductor devices. Also, I want to tell them that this course was mostly theory-based, so if you want to expand your knowledge into theory, you can try it. If I get a chance to take this course again, I would do so. This course allowed me to develop problem-solving skills while facing unknown concepts, skills in running a project, presenting results effectively to others and writing skills for documentation of results.
Individual Problem with Dr. Peter Liu
In the last semester of my master’s, I took the individual problem (IP) course under Dr. Peter Liu. The IP course was an opportunity to work in a research group called Mid Infrared and Terahertz Photonics and Optoelectronics Technologies (Mt. POET) lab. It was a valuable experience for future career opportunities. It helped me gain research experience in the university environment. I became interested in terahertz technology and optoelectronics while working with Dr. Liu. This course was divided into two parts. The first part, I worked on a project and in the second portion I helped with some ongoing lab work. This opportunity presented a chance to explore optoelectronics, trained me to use a few new types of equipment, and improved my detailed oriented working habits.
The first part of this course was about a biomimicking project of an existing organism called Diatom. Diatoms are unicellular photosynthetic algae found in places of moisture/water and light. They are also known as Jewels of the sea. They can range from 2 micrometers to 500 micrometers. There are more than 100,000 species of Diatoms known. Depending upon its size, shape, and pattern on the outermost shell called frustule made up of silica, each species has different parameters. When Diatoms die, their organic matter erodes, the silica frustule remains, and it sinks to the bottom of the water body they are inhibiting, forming a powdery substance called Diatomaceous Earth. These diatomaceous earths have commercial applications such as food products, pesticides, wine filtration units, etc. The presence of a highly symmetrical body, porous structure, silica frustule, and microscopic size makes Diatomaceous Earth a material worth investigating for future optics and photonics applications.
I worked in a group to investigate the diatomaceous earth. We started by filtering Diatomaceous Earth samples to get a particular range of sample size and remove unwanted particles. After filtration, we reviewed various processes to exfoliate Graphite to form Graphene flakes and selected sonication for it. Then, we prepared the Graphene Flakes to coat these samples with a low-power Ultrasonic bath machine using different solutions such as Acetone, Water, Isopropanol, and Ethanol.
After mixing the diatoms with graphene, we took the Fourier Transform InfraRed (FTIR) measurement for the new composite samples shown in figure 1 and the Scanning electron Microscope (SEM) images shown in figure 2. We observed a change in the optical properties of the mixture samples compared to the optical properties of just Diatomaceous Earth samples. We need a further detailed investigation into such differences, which are dependent on processes such as Graphene Flakes preparation, Mixture ratio, and concentration between Diatoms and Graphene Flake samples, Also the coating mechanism utilized.
I also worked on a literature review of surface roughness reduction in nanoscale materials which was the second part of my course. It encouraged me to read different research papers and understand them. As a result, we found many research papers indicating different methodologies to achieve the desired surface roughness in metal films. We determined the pros and cons for each method and detailed process information for the feasibility of such actions performed in the lab.
The methods usually used in the mechanical industry to reduce surface roughness, where roughness ranges from millimeter to micrometer range, didn’t work in this case. We were dealing with the nanoscale surface roughness in metal films. There are various methods to fabricate thin films, such as Vacuum deposition, Thermal Spray, Electrochemical deposition, etc., with their applications in nanoelectronics, robotics, and the aviation field.
For achieving the smooth nano metal film, the fabrication method is crucial, not just reducing the surface roughness. The surface roughness of the metal films can be reduced by controlling and optimizing various parameters during the production process. I learned from this literature review that when choosing from different production techniques, not just surface roughness but film quality, film loss, its final electrical properties, optical properties, production cost, and time are needed to be considered. The electromigration method can be beneficial and easy to perform on metal films to reduce surface roughness as a one-step process. Electrical stress applied, time of the electromigration, and the setup of the experiment plays a vital part in the surface roughness reduction in the metal film under experimentation. Figure 3 represents the results of electromigration from the paper.
While doing this course, I helped build a microscope in Mt. POET. This was my first experience in building microscope, and I cannot put the feeling in words. We used various available parts in the lab from different broken or unused parts and assembled them into a functioning microscope. There were some issues we faced during the assembly of the microscope, but we were able to rectify them. The professor did the final tuning for the proper operation. Now, there is an operating microscope in the lab. This feels good that I helped in the research lab, and I had contributed something to the lab that will be used for a long time by other students. If I get a chance to work again in the research lab, I will do it. Such opportunities led to further development of one’s mind and career possibilities.
I would recommend electrical students take an individual problem course with Dr. Liu or any other preferred research professor because it is a good research experience and will be helpful in a future research opportunity and job positions. I would suggest students take this opportunity to gain research experience and help further studies in the semiconductor industries.
EE 548 - Microelectronic device fabrication reflection
My interest in semiconductor manufacturing guided me to the course EE 548 Microelectronic Device Fabrication taught by Dr. Cheng at SUNY Buffalo. The EE 548 course was about wafer fabrication, wafer surface preparation, pattern development, and photolithography. It gave an overview of the semiconductor industry, from silicon manufacturing to commercial products.
There was only one assignment in this course given by professor and there were three students in my group. This group project was a good learning experience of semiconductor industry processes. The project topic was to develop a new NAND gate IC as shown in figure 1. We needed to make an in-principal process design for manufacturing the NAND gate circuit on a silicon wafer.
In this project, we had to design the individual transistor and diode, formulate the general layout of the circuit design, separate the layers into manufacturing steps, and design the needed photo mask(s). Given NAND gate IC consisted of several transistors, diodes, and sometimes resistors. The goal was to reduce the number of components in the circuit without hampering its functionality. After brainstorming for a few circuit designs and testing them using simulation software, we compared all circuit designs to see the total number of components and any changes in functionality.
We designed the individual transistors and diodes for the required circuit. We used Electronic Design Automation (EDA) tools to prepare and present the final circuit design during the presentation. An EDA tool, microwind for designing the structured layers of semiconductor, we demonstrated and explained all the results and simulations to the professor and other students.
Steps in photolithography
It starts with wafer cleaning then a silicon oxide layer gets deposited as a barrier layer on the silicon wafer. In the next step, the photoresist gets applied to the silicon wafer then the wafer gets soft-baked. The photomask gets aligned with the wafer. The photomasks can be of two types, either a positive photomask or a negative photomask which will create a hole or island on the wafer, as shown in figure 3.
After properly aligning the mask, then it gets exposed to UV light. The UV light passes through the photomask, and the pattern gets printed on the wafer. Then the wafer gets hard-baked. In the next step, etching by the dry or wet method to remove the exposed pattern on a silicon wafer. The silicon wafer gets doped by diffusing the p-type or n-type materials in the exposed area. Figure 4 represents the overall flow of the photolithography process.
The photoresist gets removed, then the metallization on the silicon wafer will take place in which metal contacts get attached to the Integrated Circuit (IC) pins. The designed IC gets tested to ensure its proper working, and the failed IC gets discarded. The good IC gets assembled and packed.
A few of the learning points during this course that may arise included the ability to use any system for presentations and being prepared for any technical issues, so that they will not affect the flow of your presentation. Our group had a few technical issues when presenting the slide. This was a good learning experience which encouraged us to think on our feet. Even though the problem statement was somewhat similar for students, each student’s approach to it was different and had used different software’, and professor made it clear that there was no wrong approach.
If I had to do it again, I would. The semiconductor manufacturing industry is essential for any electronic product. The manufacturing industry has evolved from regular scale to micro scale, now on the nanoscale. Emerging technologies are changing the fabrication process depending on demand and needs.
I would recommend electrical students to take this course to get more detailed knowledge about the semiconductor industry. This experience gave me the actual problem in the semiconductor industry and not just the theoretical knowledge. My interest in semiconductor manufacturing became more substantial, and I finally had a course that taught me the industrial process for the fabrication of devices.