NIST Technique Measures Noise Figure of CMOS Devices on Wafer

The noise figure of semiconductor devices used in devices such as TV tuners and cell phones are a critical factor in determining the sensitivity and performance of this equipment. The National Institute for Standards and Technology (NIST), says that until now, it has been difficult to measure the noise figures of CMOS devices accurately over much of their signal range (1 - 10 GHz), making it difficult to obtain an optimum match to antennas and other circuitry, resulting in significant signal loss.

A team of NIST researchers working with the IBM Semiconductor Research and Development Center in Essex Junction, Vt., developed improved methods for accurately measuring the very faint thermal noise caused by the random motion of electrons in electronic circuits. The technique can be used to reliably measure the noise in CMOS devices before they are cut from silicon wafers. NIST said it believes this to be the first method for on-wafer noise measurements that directly links to national standards for thermal noise power.

The team demonstrated the use of "reverse noise" measurements focusing on noise emitted from the input of the transistor when incoming signals are reflected and scattered as a tool for checking overall noise parameters. NIST said this method "can improve precision, particularly of the optimal impedance properties needed in transistors to minimize noise."

The measurement methods were described at the IEEE Radio Frequency Integrated Circuits Symposium in San Francisco June 12 and are summarized in the latest NIST Tech Beat article Noise Measurement May Boost Cell Phone Performance.