Víctor H. Champac

CURRENT VS. LOGIC TESTING OF GATE OXIDE SHORT, FLOATING GATE AND BRIDGING FAILURES IN CMOS

Logic testing has s o m e well known l imi ta t ions f o r circuits with failures causing intermediate voltage levels or, even , correct logic outputs with parametric deuiat ions f r o m the fault free specificattons. For these failures current testing might be considered as a complementary technique t o logic testing. I n this work, these physical defects widely encountered i n ioday’s CMOS processes, are modelled taking into account t h e topology o f the defective circuit and the parameters o f the technology used. These models are used to simulate a t electrical level (SPICE) the behaviour of a simple three inver ter chain wi th a f au l t y inverter. T h e merits o f current testing in f ront of voltage testing are studied for the classes of defects modelled.

Electrical model of the floating gate defect in CMOS ICs: implications on I/sub DDQ/ testing

The behavior of an MOS transistor with an open in the polygate path (floating transistor gate defect) is investigated and its effect on the quiescent power supply current I/sub DDQ/ is studied. The possible detection of this defect by current testing is explored in fully complementary CMOS circuits. The behavior of a transistor with its floating gate is modeled using the coupling capacitances in the floating gate and the charge in the transistor gate. The poly-bulk and metal-poly capacitances are found to be two significant parameters in determining the degree of conduction on the affected transistor. The induced voltage in the floating gate and the quiescent current are estimated by analytical expressions. The model is compared with SPICE 2 simulations. Good agreement is observed between the simple analytical expressions, simulations and experimental measures performed on defective circuits. In addition, it is shown that the floating gate transistor can be modeled as a weakly conductive stuck-on transistor or as a stuck-open transistor depending on the values of the parameters characterizing the defect. >

Quiescent current analysis and experimentation of defective CMOS circuits

Physical defects widely encountered in todays CMOS processes (bridges, gate oxide short (gas) and floating gates) are modeled taking into account the topology of the defective circuit and the parameters of the technology. These models are used to simulate at electrical level the behavior of a simple 3-inverter chain with a defective inverter. The results are compared with experimental data of integrated circuits fabricated with intentional defects. The influence of the characteristics of each defect on IDDQ has been investigated by electrical simulation and experimentation.

Adaptive Error-Prediction Flip-flop for performance failure prediction with aging sensors

This paper presents a new approach on aging sensors for synchronous digital circuits. An adaptive error-prediction flip-flop architecture with built-in aging sensor is proposed, performing on-line monitoring of long-term performance degradation of CMOS digital systems. The main advantage is that the sensors performance degradation works in favor of the predictive error detection. The sensor is out of the signal path. Performance error prediction is implemented by the detection of late transitions at flip-flop data input, caused by aging (namely, due to NBTI), or to physical defects activated by long lifetime operation. Such errors must not occur in safety-critical systems (automotive, health, space). A sensor insertion algorithm is also proposed, to selectively insert them in key locations in the design. Sensors can be always active or at pre-defined states. Simulation results are presented for a balanced pipeline multiplier in 65 nm CMOS technology, using Berkeley Predictive Technology Models (PTM). It is shown that the impact of aging degradation and/or PVT (Process, power supply Voltage and Temperature) variations on the sensor enhance error prediction.

Low-sensitivity to process variations aging sensor for automotive safety-critical applications

In this paper, circuit failure prediction by timing degradation is used to monitor semiconductor aging, which is a safety-critical problem in the automotive market. Reliability and variability issues are worsening with device scaling down. For safe operation, we propose on-chip, on-line aging monitoring. A novel aging sensor (to be selectively inserted in key locations in the design and to be activated from time to time) is proposed. The aging sensor is a programmable delay sensor, allowing decision-making for several degrees of severity in the aging process. It detects abnormal delays, regardless of their origin. Hence, it can uncover “normal” aging (namely, due to NBTI) and delay faults due to physical defects activated by long circuit operation. The proposed aging sensor has been optimized to exhibit low sensitivity to PVT (Process, power supply Voltage and Temperature) variations. Moreover, the area overhead of the new architecture is significantly less than the one of other aging sensors presented in the literature. Simulation results with a 65 nm sensor design are presented, ascertaining its usefulness and its low sensitivity, in particular to process variations.

Predictive error detection by on-line aging monitoring

The purpose of this paper is to present a predictive error detection methodology, based on monitoring of long-term performance degradation of semiconductor systems. Delay variation is used to sense timing degradation due to aging (namely, due to NBTI), or to physical defects activated by long lifetime operation, which may occur in safety-critical systems (automotive, health, space). Error is prevented by detecting critical paths abnormal (but not fatal) propagation delays. A monitoring procedure and a programmable aging sensor are proposed. The sensor is selectively inserted in key locations in the design and can be activated either on users requirement, or at pre-defined situations (e.g., at power-up). The sensor is optimized to exhibit low sensitivity to PVT (Process, power supply Voltage and Temperature) variations. Sensor limitations are analysed. A new sensor architecture and a sensor insertion algorithm are proposed. Simulation results are presented with a ST 65 nm sensor design.

Detectability conditions for interconnection open defects

The detectability of interconnection opens by logic and I/sub DDQ/ testing is investigated. Opens in interconnection paths disconnect the driven gate(s) from the driving gate. An electrical model for interconnection opens is used to predict the detectability of this type of open. Using the proposed model, explicit analytical expressions have been obtained to determine the conditions for reliable detection of this defect by logic and I/sub DDQ/ testing. The cases of full controllability and non-full controllability of the signals at the coupling lines have been analysed. The effect of the trapped charge during fabrication has also been investigated. In addition, it has been found that the detectability of interconnection opens depends on the metal level where the signals are laid-out. The detectability dependency of interconnection opens on the test generation process has been analyzed.

Programmable aging sensor for automotive safety-critical applications

Electronic systems for safety-critical automotive applications must operate for many years in harsh environments. Reliability issues are worsening with device scaling down, while performance and quality requirements are increasing. One of the key reliability issues is long-term performance degradation due to aging. For safe operation, aging monitoring should be performed on chip, namely using built-in aging sensors (activated from time to time). The purpose of this paper is to present a novel programmable nanometer aging sensor. The proposed aging sensor allows several levels of circuit failure prediction and exhibits low sensitivity to PVT (Process, power supply Voltage and Temperature) variations. Simulation results with a 65 nm sensor design are presented, that ascertain the usefulness of the proposed solution.

Built-in aging monitoring for safety-critical applications

Complex electronic systems for safety or mission-critical applications (automotive, space) must operate for many years in harsh environments. Reliability issues are worsening with device scaling down, while performance and quality requirements are increasing. One of the key reliability issues is to monitor long-term performance degradation due to aging in such harsh environments. For safe operation, or for preventive maintenance, it is desirable that such monitoring may be performed on chip. On-line built-in aging sensors (activated from time to time) can be an adequate solution for this problem. The purpose of this paper is to present a novel methodology for electronic systems aging monitoring, and to introduce a new architecture for an aging sensor. Aging monitoring is carried out by observing the degrading timing response of the digital system. The proposed solution takes into account power supply voltage and temperature variations and allows several levels of failure prediction. Simulation results are presented, that ascertain the usefulness of the proposed methodology.

Testability of floating gate defects in sequential circuits

The logic detectability conditions of floating gate (FG) defects in sequential circuits are considered. It has been found that a FG defective sequential circuit may be able to memorize one or two logic states depending on the values of the defect parameters. I/sub DDQ/ testing may detect a large class of floating gate defects including some defective transistors located in logically untestable branches. Good agreement is observed between the theoretical and simulated results with experimental measurements performed on a typical scan path cell designed intentionally with floating gate defects.