Reliability Diagnostic Methods By Means Of Noise In Semiconductor Devices

MOS devices have to suffer from ionizing radiation as they are widely used in theenvironment of space, nuclear energy and nuclear weapon. The parameter defradation,half and /or full permanent damage even failure in function of MOS devices will occurdue to the generation of radiation-induced oxide trapped charges and interface traps. Inorder to keep the devices work well in the environment of ionizing radiation,radiation-anneal techniques of ionizing radiation are generally used. The moreimportant thing is that this method will induce some new latent defects in the deviceunder test, let alone this method is expensive, time-waste and destructive. It is thereforeuseful to consider whether a simple, fast and nondestructive method can be defined tocharacterize the ability of MOS devices to restrain radiation. As a kind of small volume,long life, no touching and anti-jamming device, Optoelectronic Coupled Devices(OCDs) are widely used in the military affairs and spaceflight. Its noise has arelationship with inner defects, and affects its reliability, even functions. So study ofOCDs'noise will be helpful to probe defects in these devices, especially to inspect theinfluence of latent defects to the devices'performances.The method of characterizing ability of MOS devices to restrain radiation isthoroughly studied by analyzing the relationship between 1/f noise and radiation effects.The non-stationary 1/f noise in MOS devices is also studied thoroughly. Based on thecharacteristics of 1/f noise in OCDs, the method of evaluating OCDs'reliability by 1/fnoise is developed, and obtains valuable results as following:1,A low frequency noise testing and analyzing system of electronic device, basedon the idea of virtual instrumentation, is set up in the first time. Base on this system, 1/fnoise in MOSFETs,with different channel area and types, are tested. Reasons of 1/fnoise differences between nMOSFETs and pMOSFETs are analyzed in theory, whichinclude (1) the potential barrier of an electron and a hole in oxide are not same.Meanwhile, the efficiency matter of an electron is bigger than a hole. (2) The density oftraps is bigger near the bottom of conduct band than near the top of value band. (3) Inthe same condictions,electrons are faster than holes under the same conductions.2,Experimental results demonstrate that the magnitude of 1/f noise in switchingbiased MOSFETs is smaller than in constant biased, the reduction becomes large withthe device biased to further inversion and is proportional to the frequency of biasvoltage. A nonstationary 1/f noise model in MOSFETs is developed. Simulated Resultsfrom this mode by the method of Monte Carlo demonstrate that the reduction ofnonstationary 1/f noise is due to the modulation of exchanges between oxide traps andcarriers, which is induce by bias voltage.3,The radiation experiments of MOSFETs, with different channel area and type,have been made using 60 Coγas radiation source. The results demonstrate that thereare obvious relationships between 1/f noise of pre-radiation and the changes ofthreshold voltage and transconductance after radiation. The results from theorydemonstrate that trapped charges induced by radiation come from oxide cavities (≡Si··Si≡)and tri-value silicon(Si3=Si·), the former transforms into E' center whichis the main physical construction of oxide traps, and the latter is p b center which is themain physical construction of interface traps. These defects are the same origin asdefects that cause the 1/f noise. The results also tell that the magnitude of 1/f noisebecomes large with the dose of radiation adding, which predicates the more tappedcharges induced by radiation and its distribution is also changed.4,Based on the mechanisms of fluctuations of carriers number and velocity, aunified 1/f noise model in MOSFETs is developed, including the traps distribution andtwo manners of traps communicate carriers with channel, tunneling and thermalactivation. Methods of extracting distribution of oxide traps and interface traps by 1/fnoise are discussed according to this unified model. The results calculated from thismodel and experiments demonstrate that the distribution of oxide traps is a shape as "U"in the energy space and a positive exponent shape in the geometry space. The radiationnot only adds the oxide traps , but also change its distribution into negative exponent ingeometry space.5,A quantitative model of characterizing ability of MOS devices to restrainradiation by 1/f noise pre-radiation is developed. Methods of predicating changes ofthreshold voltage and transconductance are thoroughly studied, which can be used toscreen MOSFETs more severely.6,Measurement results of 1/f noise in OCDs b after a large and long timeelectrical stress demonstrate that there are the similar rule of 1/f noise changes withinput current, but comparing to virgin device, the magnitude of 1/f noise in the stresseddevice increases about 7 times. It is discussed that the increasing magnitude of 1/f noiseis due to new traps induced by electrical stress. 1/f noise under different bias revealsdifferent characteristics of defects in OCDs.7,Models of 1/f noise and G-R noise for OCDs are developed. The resultsdemonstrate that G-R noise source in OCDs lies in the photosensitive transistor. Basedon these experimental and theoretical results, the method of evaluating OCDs'reliabilityby 1/f noise is discussed.All these results will give a experimental and theoretical base for 1/f noise to beused in evaluating semiconductor reliability.