Reliability and MTTF evaluation of a repairable complex system under waiting

This paper deals with the reliability and mean time to failure (MTTF) evaluation of a complex system under waiting incorporating the concept of hardware failure and human error. Failure rates of the complex system follow exponential time distributions, whereas repair follows a general repair time distribution. Laplace transforms of various state probabilities have been evaluated and then reliability is obtained by the inversion process. A formula for variance of time to failure has also been developed. A particular case is also given to highlight some important results. Moreover, various plots have been sketched at the end.     

A two-unit standby power plant with imperfect switching

The reliability and MTTF of a complex system consisting of two generators connected in standby redundancy are evaluated. The object of the system is to supply power generated by a generator from a power-house to critical consumers connected by imperfect cables and switches. The reliability and MTTF have been evaluated by Boolean function technique.     

An algebraic method for reliability calculations

This paper evaluates the reliability behaviour of a complex system consisting of three sub-systems G₁, G₂ and G₃ connected in parallel redundancy (1-out-of-3: G). These sub-systems are nothing but three power generators in a power house which are connected with switching devices. By the application of Boolean function technique and the theorem of summation of probabilities of compatible events, a symbolic expression for reliability of such a complex system has been evaluated by considering that failure times for various components of the complex system follow arbitrary distributions. In particular, reliability has been evaluated for exponential and Weibull distributions. Moreover, an important parameter, viz. MTTF, has also been computed for exponential failure rates of the units comprising the system. A numerical example, along with graphs, is discussed at the end to highlight the important results.     

Reliability analysis of a two state repairable parallel redundant system under human failure

In this paper, the investigations have been carried out for the MTTF and reliability analysis of a repairable two-unit redundant electronic equipment having two states under human failures. The two-unit repairable parallel redundant system suffers two types of failures; viz; unit failure and human failure. Human failure brings the system to a complete failure stage. There is only one server who is always available. Laplace transforms of the probabilities of the complex system being in up and down states have been derived and have been inverted to obtain time dependent probabilities. Two graphs have also been given in the end.     

MTTF and availability evaluation of a two-unit, two-state, parallel redundant complex system with constant human failure

This paper deals with MTTF and availability analysis of a two-state complex general repairable system consisting of two units arranged in parallel. Single service facility is available for the service of unit failure. The failure and repair times for the system follow exponential and general distributions respectively. Laplace-transforms of the various state probabilities have been derived and steady state behaviour of the system has also been examined. Availability at any time is obtained by the inversion process. To make the system more compatible with the physical situation, MTTF for the system has also been evaluated and various graphs have been plotted to highlight the utility of the model.     

Reliability analysis of k-out-of-n systems with partially repairable multi-state components

In some environments the components might not fail fully, but can lead to degradation and the efficiency of the system may decreases. However, the degraded components can be restored back through a proper repair mechanism. In this paper, we present a model to perform reliability analysis of k-out-of-n systems assuming that components are subjected to three states such as good, degraded, and catastrophic failure. We also present expressions for reliability and mean time to failure (MTTF) of k-out-of-n systems. Simple reliability and MTTF expressions for the triple-modular redundant (TMR) system, and numerical examples are also presented in this study.     

Reliability and availability analysis of on surface transit systems

This paper presents four Markov models pertaining to repairable and non-repairable on surface transit systems. The expressions for state probabilities, system reliability, mean time to failure (MTTF) and steady state availability are developed. System reliability, MTTF and steady state availability plots for various assumed values of system parameters are shown.     

Reliability of laser-induced metallic vertical links

A new method has been proposed to form electrical connections vertically between two levels of metallization by using a commercial pulsed IR laser system. Samples were stressed at accelerated current densities and temperatures. The failure activation energy has been found to be about 0.66 eV, from which electromigration is identified as a main failure mode. The extrapolated mean time to failure (MTTF) at room temperature and accelerated current density of 3 MA/cm² is about 38 years. The dependence of MTTF on laser energy has also been obtained, showing agreement with the resistance dependence on laser energy. Focused ion beam (FIB) cross sections suggest that the laser process-induced voids in the lower line limit the lifetime of links. Furthermore, a modified structure is proposed to improve the electromigration reliability. From the reliability point of view, this study shows that the laser-induced vertical link has sufficient reliability for practical implementation     

Reliability and availability analysis of transit systems

This paper presents three newly developed Markov models representing on-surface transit systems. Transit system reliability, steady-state availability, mean time to failure (MTTF) and variance of time to failure formulas are developed. Selective plots are shown for each model. These plots clearly exhibit the impact of various parameters on transit system reliability, steady-state availability, and MTTF.     

A simple Markovian method for MTTF calculation

The MTTF of a system design with constant failure and repair rates and with some forms of stand-by redundancy and switching is an important characteristic of the system. Commonly, calculation of the MTTF requires knowledge of the reliability function R(t), which is integrated to yield the MTTF. In many cases obtaining the reliability function is a non-trivial task and its analytic integration may be quite tedious. In the following we describe a simple method of obtaining the MTTF of such systems which avoids the need of knowledge of R(t). The method is Markovian in nature and is based on summing the probabilities of all the possible routes (in the space of states) by which the system can get from its initial state at t = 0 to an absorbing state (failed state), where each such probability is multiplied by the average time required for the system to follow that route. This weighted sum yields the MTTF for any given initial conditions. The method is demonstrated on some useful systems and analytical formulas for the MTTF are derived. It is further demonstrated how the results of the method may be used in the calculation of the MTBF of the system in steady-state.     

Estimation of system reliability for uncooled optical transmittersusing system reliability function

This paper investigates the system reliability for 155 Mb/s optical transmitters by deriving a system reliability function from reliability data of each component for transmitters, laser diode, photodiode, optical assembly, and driver IC. The reliability data for each component reliability function have been obtained from accelerated aging test. The reliability parameters such as failure rate, mean time-to-failure (MTTF), standard deviation are obtained from a probability plotting method. From the system reliability function, the MTTF of the optical transmitter at 65°C was estimated to be 47000 h with 95% confidence. In this estimation, we introduced modified lifetime of laser diodes and reliability function of optical assembly     

Reliability and M.T.T.F. analysis of a power plant consisting of three generators by Boolean Function technique

This paper investigates the reliability behaviour of a non-repairable parallel redundant complex system which is nothing but a power plant. The object of the system is to supply power generated by three generators from a power house to a very critical consumer, connected by cables and switches etc. The reliability of the power supply to the critical consumer has been obtained by using the Boolean Function technique. Moreover, an important parameter of reliability, viz. M.T.T.F. (mean time to failure), has also been computed for exponential failure rates of components. A numerical example with graphs has also been appended in the end to highlight the important results.     

Goal-seeking problem in discrete event systems simulation

For most complex stochastic systems such as microelectronic systems, the Mean Time To Failure (MTTF) is not available in analytical form. We resort to Monte-Carlo Simulation (MCS) to estimate MTTF function for some specific values of underlying density function parameter(s). MCS models, although simpler than a real-world system, are still a very complex way of relating input parameter(s) to MTTF. This study develops a polynomial model to be used as an auxiliary to a MCS model. The estimated metamodel is a Taylor expansion of the MTTF function in the neighborhood of the nominal value for the parameter(s). The Score Function methods estimate the needed sensitivities (i.e. gradient, Hessian, etc.) of the MTTF function with respect to the input parameter in a single simulation run. The explicit use of this metamodel is the target-setting problem in Taguchi's product design concept: given a desired target MTTF value, find the input parameter(s). A stochastic approximation algorithm of the Robbins-Monro type uses a linear metamodel to estimate the necessary controllable input parameter within a desired accuracy. The potential effectiveness is demonstrated by simulating a reliability system with a known analytical solution.     

Computing steady-state mean time to failure for non-coherent repairable systems

Mean time to failure (MTTF) is an important reliability measure. Previous research is mainly concerned with the MTTF computation of coherent systems. In this paper, we derive equations to calculate the steady-state MTTF for noncoherent systems. Based on the equations, we extend the BDD by adding an intersection edge in each BDD node to efficiently store additional information for MTTF computation of noncoherent systems. A recursive algorithm is developed for MTTF computation using the extended BDD. To accelerate building the extended BDD, a method is proposed to avoid calculating the intersection edge for some nodes by keeping node monotonicity during the BDD construction. We show the efficiency of our algorithm by applying it to some example fault trees, real-life applications, and large fault tree benchmarks.     

Stochastic analysis of outdoor power systems in fluctuating environment

This paper presents newly developed expressions for state probabilities, system reliability, system availability and mean-time-to-failure (MTTF) for three types of outdoor electric power systems working in random environment. System measure plots are shown for all these Markov models.     

A note on the cost analysis of an n-unit system with spares

This paper deals with the cost analysis of a non-repairable standby system consisting of (n + m) identical units; n-units are needed for the system to function, while the remaining m units are warm standbys. The online and standby units have different constant failure rates. There is no facility for repair. Functions expressing the probability that in (0, t) there are i on-line failures and j standby failures and thereby the reliability of the system. MTTF and the expected profit are obtained. Finally, a numerical example with graphs is also given to highlight important results like the reliability of the system, MTTF and the expected profit.     

GaAs微波功率FET可靠性评价技术研究

为了使GaAs微波功率FET更可靠地应用于重要微波系统，选取高可靠器件生产线生产的CS0531型器件进行加速寿命试验，并研制了专用试验设备。观察到器件n因子随着试验时间有增大的趋势，初始低频噪声值与器件突然烧毁有一定的相关性。这一结果表明低频噪声有可能成为未来评价GaAs器件可靠性的一种方法。该器件失效机构激活能2．45eV，为道温度110℃时，10年平均失效率4Fit，平均寿命75137×1011h。     

Time dependent breakdown characteristics of parylene dielectric in metal–insulator–metal capacitors

In this work, we present reliability results of MIM (Metal–Insulator–Metal) capacitors fabricated with parylene as the dielectric, deposited at room temperature. We have evaluated the time dependent dielectric breakdown (TDDB) of parylene-based MIM capacitors as a function of constant DC voltage stress, area and dielectric thickness of the capacitor. Mean-time-to-failure (MTTF) of parylene evaluated at different stress voltages shows a power law distribution over the applied voltage range and device area, with MTTF driven by the number of defects. Defect density in the parylene capacitors is also reported and is calculated to be ～1.2 × 10³ defects/cm².     

Instruction-Vulnerability-Factor-Based Reliability Analysis Model for Program Memory

Bit faults induced by single-event upsets in instruction may not cause a system to experience an error. The instruction vulnerability factor (IVF) is first defined to quantify the effect of non-effective upsets on program reliability in this paper; and the mean time to failure (MTTF) model of program memory is then derived based on IVF. Further analysis of MTTF model concludes that the MTTF of program memory using error correcting code (ECC) and scrubbing is not always better than unhardened program memory. The constraints that should be met upon utilizing ECC and scrubbing in program memory are presented for the first time, to the best of authors’ knowledge. Additionally, the proposed models and conclusions are validated by Monte Carlo simulations in MATLAB. These results show that the proposed models have a good accuracy and their margin of error is less than 3 % compared with MATLAB simulation results. It should be highlighted that our conclusions may be used to contribute to selecting the optimal fault-tolerant technique to harden the program memory.     

Acceleration factors for THB induced degradation of AlGaAs/InGaAs pHEMT devices

PHEMT devices initially showing high failure rates during Temperature Humidity Bias (THB) reliability testing were investigated further using a number of temperature and humidity conditions. Ambient temperature was varied from 85 °C to 110 °C, humidity from 65% RH (Relative Humidity) to 85% RH. Failure rates were fit to a Peck acceleration model using the method of maximum likelihood. Median time to failure (MTTF) estimates were calculated at anticipated field service conditions using the experimentally determined model parameters. The MTTF is predicted to be typically less than a year for the die variant studied. Countermeasures outside the scope of this investigation have been implemented to effectively eliminate this issue allowing RFMD to supply products with suitable reliability.