Research On Noise Measurement Technology In Medium Impedance/low Impedance Sample

As a new tool for evaluate electronic devices reliability, low frequency noise measurement are more and more recognized by researchers. Along with the continuously development in study of basic theory of low frequency noise and the advance of noise measurement technic level, study and application field of low frequency noise are more and more widely. Because of the lesser impedance in medium impedance /low impedance devices such as passive resistance devices, in really noise signal measurement, this will make the noise coefficient increased obviously, SNR will be worse in the process of signal transfer, and lead up to the augment of the system`s background noise. Therefore, how to pick-up the noise signal exactly in the medium impedance/ low impedance devices with weak noise is the urgent affairs for currently research and application in low frequency noise.Based on the analyzing of the impedance characteristics and noise level in the samples, the technology of low frequency noise measurement in medium impedance/ low impedance devices is developed, and obtains valuable results as following:1,Analysing the influence factors detailedly, impedance matching, background noise and the system`s measure precision, when measureing the noise signals in medium impedance/ low impedance devices. For measuring the noise voltage signals in the samples, the impedance of the samples matches the input impedance of the amplifier system by voltage. Thereby, the input impedance of the amplifier system should be higher than the impedance of the samples, so that the noise voltage in the samples present the lowest losing. However, the input impedance of the amplifier cannot increase without limit, too large input impedance will make the noise coefficient of the amplifier increased, the SNR will be worse in the process of signal transfer, and lead up to the raise of the system`s background noise. Consequently, this will make against the measurement of weak noise signals in the sample. The advance of the system`s measure precision will help to measure weak noise signals, this mostly depend on the advance of the gain of the amplifier system and the sampling precision.2,Based analysis of above, this thesis design and carry out the medium impedance/ low impedance devices noise measurement system which utilizes two amplifiers in series to make the signal enlarge. By choosing the preamplifier with low input resistance (1kΩ),ultra low background noise (power spectrum density grade is 10-18V2/Hz ) as the first level of amplifier system, we can solve the problem about impedance matching and background noise. The second level amplifier improves the measurement precision of measurement system by choosing high gain amplifier. Besides, in this thesis we give the outline of method to use this system.3,We testifyed many technical parameters of measurement system by manyexperiments. Experiments proved that the noise measurement system can accurately measure the noise signal in medium impedance/ low impedance sample with the impedance range from 20Ωto 100Ω, system equivalent input background noise can get down to 10-18V2/Hz,and the noise voltage measurement precision can get to 1nV. In this thesis, we also discussed the surroundings interfere influence to the measurement results.4,In this thesis, we also give two noise measurement cases, noise measurement about metal interconnect eletromigration aging process and noise measurement about low impedance thick film resistor sample. Experiments proved that this noise measurement system can pick-up the low frequency noise information accurately. In the measurement process, the white noise level of the system can stay stabilization all the time. By experiments we proved the excellent performances index and exhibited its bright apply foreground.