P. Girard

Reducing power consumption during test application by test vector ordering

This paper considers the problem of testing VLSI integrated circuits without exceeding their power ratings during test. The proposed approach is based on a re-ordering of the vectors in the test sequence to minimize the switching activity of the circuit during test application. Our technique uses the Hamming distance between test vectors and guarantees a decrease in power consumption and heat dissipation without modifying the initial fault coverage. Results of experiments are presented at the end of this paper and shows a reduction of the circuit activity in the range from 8.2 to 54.1% during test application.

Efficient scan chain design for power minimization during scan testing under routing constraint

Scan-based architectures, though widely used in modern designs, are expensive in power consumption. In this paper, we present a new technique that allows to design power-optimized scan chains under a given routing constraint. The proposed technique is a three-phase process based on clustering and reordering of scan cells in the design. It allows to reduce average power consumption during scan testing. Owing to this technique, short scan connections in scan chains are guaranteed and congestion problems in the design are avoided.

Low power BIST design by hypergraph partitioning: methodology and architectures

Power consumption of digital systems may increase significantly during testing. In this paper, we propose a novel low power/energy Built-in Self Test (BIST) strategy based on circuit partitioning. The strategy consists of partitioning the original circuit into structural subcircuits so that each subcircuit can be successively tested through different BIST sessions. In partitioning the circuit and planning the test session, the switching activity in a time interval (i.e. The average power) as well as the peak power consumption are minimized. Moreover, the total energy consumption during BIST is also reduced since the test length required to test the subcircuits is not so far from the test length for the original circuit. The proposed strategy can be applied to either test-per-scan or test-per-clock BIST schemes by slightly modifying conventional TPG structures as illustrated in this paper. Results on ISCAS circuits show that average power reduction of up to 62%, peak power reduction of up to 57%, and energy reduction of up to 82% can be achieved at a very low area cost in terms of area overhead and with almost no penalty on the circuit timing.

Electrostatic Force and Force Gradient Microscopy: Principles, Points of Interest and Application to Characterisation of Semiconductor Materials and Devices

In this paper, the physical principles of local electrical observations and measurements and related analytical formulas, as well as the optimal experimental conditions for electricalmeasurements, are first reminded. Secondly, it is shown, based on experiments and analytical expressions, how the observations obtained with the methods of force and force-gradient microscopy can be analysed. The advantage of the forcegradient microscopy over the force microscopy in better resolution and precision of measurements is demonstrated. The related analytical formulas are given, which explain the advanced capabilities of the force-gradient microscopy for precise electrical studies on local objects on the subnanometer scale. Finally, based on recent published data, the main applications of the electrostatic-force and force-gradient microscopy for analysis of materials and devices are briefly considered.

Near field imaging of a semiconductor laser by scanning probe microscopy without a photodetector

We propose an experimental method of near field optical imaging by scanning probe microscopy in which the probe itself serves as an infrared photodetector. The method providing a submicron spatial resolution is based on detection of a shift of the probe resonance related to its heating by absorbed IR radiation. The method does not require an apertured probe and can be realized with a conventional silicon probe used in atomic force microscopy. The method has been employed for visualization of infrared emission from a half-disk semiconductor whispering gallery mode laser.

Kelvin probe force gradient microscopy of charge dissipation in nano thin dielectric layers

Application of Kelvin probe force gradient microscopy (KPFGM) to visualize the local charge dissipation in thin dielectric layers is considered. By this method, the local charge behavior in nano thin SiO2, Si3N4, and LaScO3 dielectric layers has been studied. Local charging of the layers has been performed at the point contact with a conductive probe. KPFGM potential images reveal variations of the surface potential in the locally charged areas, which makes it possible to detect the injected charge and to study its behavior. Special experiments on the SiO2 layers with embedded Si-nanocrystals, when lateral spreading of injected charge had been suppressed, permitted to demonstrate high (better than 20 nm) lateral resolution of KPFGM observations. A simple electrostatic model has been developed to estimate the total amount of injected charge. The obtained estimations made it possible to control charge retention in the dielectric layer and possible leaks into the substrate. The studied dielectric layers demo...

An alternative to fault simulation for delay-fault diagnosis

Delay testing is a test procedure to verify the timing performance of manufactured digital circuits. A diagnosis process is often implemented after the detection of a fault in a circuit. Unfortunately, existing methodologies for locating delay defects on digital circuits have shown certain deficiencies. A new method for delay fault diagnosis, based on critical path tracing from a symbolic simulation, is presented. This method needs to consider only the fault-free circuit and provides perfectly reliable results. It does not require timing evaluations and can be very accurate.<<ETX>>

Determination of the noncharging electron‐beam energy on insulators

A new method allowing accurate determination of the primary electron energy corresponding to the zero charge deposition on insulators is presented. It consists in evaluating the surface voltage variations under an electron‐beam charge deposition, by means of a classical secondary electron spectrometer. Experimental data on lithography photoresists are reported. Comparison is made with classical metrology measurements, i.e., imaging profiles, and a good agreement is found. Experimental results show the angular dependence of the highest noncharge energy. A formulation of the secondary emission coefficient angular dependence is proposed and discussed versus experimental data.

Delay-fault diagnosis based on critical path tracing from symbolic simulation

A reliable method for delay fault diagnosis, based on critical path tracing from symbolic simulation of the fault-free circuit, is presented. It does not require timing evaluations and may be very accurate. The diagnosis method consists of simulation of the fault-free circuit with a six-valued logic algebra and a tracing of critical paths from primary outputs to primary inputs. The proposed method is an alternative to fault simulation. It requires no delay size based fault models and considers only the fault-free circuit. Consequently, this approach is faster, reliable, and requires less memory than conventional fault simulation. To improve the diagnosis accuracy, the concept of sensitive lines has been developed. Based on the method presented, a fast algorithm has been implemented in C++ on a SUN-SPARC workstation.<<ETX>>

Analysis of the lateral resolution of electrostatic force gradient microscopy

Signal measured by electrostatic force gradient microscopy (EFGM) is the z-gradient of the electrostatic force acting between the probe of an atomic force microscope (AFM) and the surface under study. A model is presented for calculating the z-gradient of the electrostatic interaction of the AFM probe with local charges in a dielectric layer at the surface. In the EFGM mode, the interaction of charges with only the probe tip apex should be taken into account. In this approach, a simplified expression can be derived for calculating the z-gradient of the electrostatic force. The model makes it possible to estimate the lateral resolution limit for EFGM imaging of individual charges and to simulate experimental EFGM images as a function of the tip-surface distance and the tip radius. The adequacy of the model was confirmed by quantitative simulation of the experimental EFGM images of local charges injected from the AFM probe into a planar array of Si nanocrystals in a thin SiO2 layer on a Si substrate.