Introduced in a Jan. 13, 1946 comic strip, the Dick Tracy watch contains many of the features one would like to see in portable wireless devices: voice recognition, video capability, seamless operation and an attractive appearance. In work that can potentially lead to a real-life Dick Tracy watch, researchers have built a tiny microphone on a silicon chip and have made significant progress towards building a low-power, single-chip radio. These would both be important components of a Dick Tracy watch. Using silicon micromachining, a state-of-the-art approach for making silicon materials with microscopic features, Peter Gammel and his colleagues at Bell Labs/Lucent Technologies in New Jersey built a microphone on a silicon integrated circuit, shown above. The base has marks with an approximate size of just 100 microns (0.1millimeters). (Figure courtesy Bell Labs/Lucent Technologies.)
An essential part of a single-chip radio would be a small rf (radio frequency) filter, a component that shields unwanted radio frequencies. The rf filter can also be used to protect the receiver on a phone from the transmitter on the phone. In current cell phones, the rf filter, made of a ceramic material, is by far the largest single component. The figure above shows a penny, a conventional ceramic filter and a new miniature RF filter, made of aluminum nitride on a silicon surface, constructed by the Lucent researchers. (Figure courtesy Bell Labs/Lucent Technologies.)
This final picture shows a "tank circuit," also built by silicon micromachining techniques, which includes an electronic component known as an inductor. An inductor is a simple loop of wire that helps determine the proper frequency for communications. The inductor is warped away from the silicon surface like a taco. The two flat plates at the left of the picture comprise a micromachined version of a capacitor, a device that stores electric charge. The two together determine a frequency that is proper for communications. For this structure, the frequency is equal to the 1960 MHz required for communications using the worldwide cellular PCS network. (Figure courtesy Bell Labs/Lucent Technologies; special thanks to Peter Gammel of Bell Labs/Lucent Technologies for supplying the figures and much of the text.)
This research is being reported at the 120th semi-annual meeting of the New York State Section of the American Physical Society at Lucent Technologies on April 23-24, 1999.