Exploration 1B: Comparing Macroscopic and Microscopic Circuit Components


These are examples of capacitors used in wired circuits. Capacitors are characterized by their ability to store a charge and then release that charge when it is needed. A capacitor in your car allows time-delayed shutoff of interior lights after the door is shut. Televisions use a capacitor to provide the current to display an image almost as soon as the switch is turned on. Can you think of other everyday places that capacitors might be used?
Capacitors consist of layers of conducting (usually metallic) layers sandwiched with insulating layers. In this example 2 layers each of thin metal foil and insulating paper are stacked alternately. The stack is then rolled (like a jelly roll) producing a cylinder with the alternating layers. The number of insulating layers, their inherent insulating ability, and the thickness of each layer combine to determine the capacitance, or strength, for the capacitor.
This metal-oxide semiconductor (MOS) capacitor from an integrated circuit shows how the layer concept is applied to the microelectronic capacitor. Can you predict which are the conducting and insulating layers? To check your predictions, you should watch the movie "Making a Capacitor." Approximately how thick is the insulating layer between the conductors?



Resistors for macroscopic circuits come in a wide variety of sizes. Resistors control the amount of current in a circuit.
Resistors are constructed many different ways. The common theme is that current flow through the circuit is retarded by a region with a lower ability to conduct. In this illustration the current flowing through the wire is reduced by a mixture of conducting and insulating solids.
Current flows through the p- region of this integrated circuit resistor. Resistance arises from the smaller cross-section of the p-region in the center. The current cannot cross over to the n- region. The gray posts are metal contacts to connect to circuitry.


A diode will only allow current to flow in one direction. Diodes are used in applications where one wants to control the polarity of current such as in converting alternating current (AC) to direct current (DC). Light-emitting diodes and photodiodes are used to transmit and receive light of specific wavelengths.
This is a cartoon cross-section of a diode like those pictured above. The colored area marked n-has excess electrons; the colored area marked p- has a deficiency of electrons. The basis for a modern diode's unidirectional nature is the fact that current flows much more efficiently from an n- region to a p- region, and not the other way.
In the diode components of integrated circuits, the p- and n- regions are retained. Since the entire component is embedded in n-type Si, the n region of the diode is more heavily modified (n+). The gray cylinders on the surface are metal contacts which, in a complete circuit, would protrude through an insulating layer to connect the diode to the rest of the circuit.
Light-emitting diodes such as this one are common components of home electronics kits. In this specialized kind of diode, light is emitted when the electrical current flows.


These transistors will be individually wired to a circuit board, for example in an old transistor radio. Internally, they are constructed very similarly to microelectronic transistors. They just have pieces large enough to be cut and assembled with machines.
The metal-oxide semiconductor (MOS) transistor used in integrated circuits revolutionized the electronics industry. It is constructed of silicon, regions of doped (modified) silicon, silicon dioxide, and metal conductors which have sub-micrometer dimensions. Do you know the functions of the different layers? Do you know how chemistry is used to build this? Find out by viewing the movie "Making a Transistor."

Comparing Macro and Micro Electronic Circuit Components | Computer Chip Thermochemistry | ChemConnections