“Smaller Than the Eye Can See: How Your Computer is Made” is a three week course (two hours per day) designed for the PEOPLE program at the University of Wisconsin-Madison. Each summer since 2003, this course has been presented to ~15 high school juniors. The course was originally designed by the Ediger, de Pablo, and Nealey research groups. Since then, students from many groups in the Chemistry Department have contributed to refining our curriculum. Our overall goals are: 1) encourage interest in science and engineering disciplines; 2) hone science and math skills that will be useful in college. We elected to organize the course around a technology theme (computers) because we judged that this approach might interest the students more than a course restricted to chemistry, physics, materials, or some other single discipline. While this technology theme provide a narrative story line for the course, we also present related material that we feel furthers our goals.
This course is composed of five inter-related modules:
- Powers of Ten – Modern computers employ chips manufactured with very small elements. On state-of-the-art chips, an individual transistor is around 14 nanometers. The first day of this course reviews manipulations involving powers of ten and the metric system of units for length. The goal is for students to develop some appreciation for the micrometer and nanometer units.
- Polymers – The process of making a computer chip utilizes photolithography. Current photoresists are polymers whose solubility properties are altered when the photoresist is exposed to light. In order to prepare the students for understanding photolithography, the polymer module communicates important concepts. (Keep in mind that some of the students have already had high school chemistry while others have not.) These concepts include covalent bonding, polymer structure, and the crosslinking of polymers. Several laboratory activities show how the properties of polymers change with crosslinking (crosslinking changes solubility and is one possible mechanism for photolithography). Other activities measure the density of various polymers and the effect of temperature on polymer elasticity. There is a discussion of polymer recycling in the context of recycling the polymer components of computers.
- Electronics – Computer operations are performed with electrical circuits. This module provides a basic introduction to circuits, including voltage, current, resistance, Ohm’s law, alternating current, and direct current. One activity is the construction of a circuit board containing several LEDs. Another activity involves the use of LEDs, incandescent and stereo speakers to examine the properties of alternating current, direct current, and frequency.
- Binary – Computer operations are done in binary and information is stored by computers in a binary format. This module introduces students to the idea of base 2 arithmetic. The students encode a message in binary using the polarity of magnets to represent zeroes and ones. This is both a visual representation of data storage and a crude illustration of how a hard drive stores information. Students also explore how hard drives are constructed and how data is stored on CDs and DVDs. A laser diffraction activity allows an estimate of the spacing between bits on CDs and the approximate storage capacity of a CD can be calculated from this spacing. A final activity explores the properties of logic gates using computer chips and an electronics breadboard. Such gates are essential to the operation of computers and nicely illustrate how operations are performed in binary.
- Photolithography – Students learn about the process of photolithography in the context of manufacturing a computer chip. The idea of lithography is introduced with an activity utilizing imprint lithography. In an activity that illustrates the principles of computer chip manufacture, the students attach a mask to a glass slide covered with a photoresist. After exposing the assembly to UV light, the slide is developed and a visible pattern is apparent in the photoresist. Single crystals of silicon are essential for manufacturing computer chips. Another activity illustrates the single crystal nature of a silicon wafer; students attempt to break the wafer along specific directions in order to establish to position of crystal planes.