A design-for-testability method and an electrical interconnect test method are proposed to detect open defects occurring at interconnects among dies and input/output pins in 3D stacked ICs. As part of the design method, an nMOS and a diode are added to each input interconnect. The test method is based on measuring the quiescent current that is made to flow through an interconnect to be tested. The testability is examined both by SPICE simulation and by experimentation. The test method enabled the detection of open defects occurring at the newly designed interconnects of dies at experiments test speed of 1MHz. The simulation results reveal that an open defect generating additional delay of 279psec is detectable by the test method at a test speed of 200MHz beside of open defects that generate no logical errors.

In this paper, the scan chain ordering method for BIST-aided scan test for reducing test data and test application time is proposed. In this work, we utilize the simple LFSR without a phase shifter as PRPG and configure scan chains using the compatible set of flip-flops with considering the correlations among flip-flops in an LFSR. The method can reduce the number of inverter codes required for inverting the bits in PRPG patterns that conflict with ATPG patterns. The experimental results for some benchmark circuits are shown to present the feasibility of our test method.

A new IDDQ testable design method is proposed for static CMOS PLA circuits. A testable PLA circuit of NOR-NOR type is designed using this method. It is shown that all bridging faults in NOR planes of the testable designed PLA circuit can be detected by IDDQ testing with 4 sets of test input vectors. The test input vectors are independent of the logical functions to be realized in the PLA circuit. PLA circuits are designed using this method so that the quiescent supply current generated when they are tested will be zero. Thus, high resolution of IDDQ tests for the PLA circuits can be obtained by using the testable design method. Results of IDDQ tests of PLA circuits designed using this testable design method confirm not that the expected output can be generated from the circuits but that the circuits are fabricated without bridging faults in NOR planes. Since bridging faults often occur in state-of-the-art IC fabrication, the testable design is indispensable for realizing highly reliable logic systems.

A procedure to remove redundancies in sequential circuits is proposed using strongly unreachable states, which are the states with no incoming transitions. Test generation is used to find undetectable faults related to two or more strongly unreachable states. Experimental results show the new procedure can find more redundancies of sequential circuits.

This paper proposes a method for testing delay faults using a boundary scan circuit in which a time-to-digital converter (TDC) is embedded. The incoming transitions from the other cores or chips are captured at the boundary scan circuit. The TDC circuit is modified to set the initial value for a delay line through which the transition is propagated. The condition for measuring timing slacks of two or more paths is also investigated since the overlap of the signals may occur in the delay line of the TDC in our boundary scan circuit. An experimental IC with the TDC and boundary scan is fabricated and is measured to estimate the delay of some paths measured by the TDC embedded in boundary scan cells. The simulation results for a benchmark circuit with the boundary scan circuit are also shown for the case that timing slacks of multiple paths can be observed even if the signals overlap in the TDC.

Retiming is a technique to resynthesize a synchronous sequential circuit by rearranging flip-flops. In view of logic optimization, retiming can potentially derive a circuit which is more simplified and testable because retiming can convert several sequential redundancies into combinational redundancies. Retiming methods proposed before have no guarantee to generate the same output sequences when the circuit start from a specified initial state such as the reset state. If the circuit with a specified initial state must have the same output sequences after retiming, rearrangement of flip-flops should be restricted. This paper presents a retiming method for circuits with a specified initial state so that retimed circuits give the same output sequences of the original circuits for any input sequences. In the proposed method, during the procedure of retiming each flip-flop keeps a value corresponding to the initial state and unification of flip-flops with different value is avoided. Our procedures uses 5-valued logic on gate level implementation to describe and calculate the values of flip-flops. Therefore after optimization using our method, the circuit has completely the same behavior as that of the original. Experimental results for ISCAS'89 benchmark circuits show the method can be used to optimize the circuits as well as a method without considering the initial state. And testability of the retimed circuit is more enhanced than that of the original circuit.

In this paper, a useful technique is proposed for realizing high speed IDDQ tests. By using the technique, load capacitors of the CMOS logic gates can be charged quickly, whose output logic values change from L to H by applying a test input vector to a circuit under test. The technique is applied to built-in IDDQ sensor design and external IDDQ sensor design. It is shown experimentally that high speed IDDQ tests can be realized by using the technique.

In this paper, a new test method is proposed for detecting open defects in CMOS logic ICs. The method is based on supply current of ICs generated by supplying time-variable supply voltage and electric field from the outside of the ICs. Also, test input vectors for the test method are proposed and it is shown that they can be generated more easily than functional test methods based on stuck-at fault models. The feasibility of the test is examined by some experiments. The empirical results promise us that by using the method, open defects in CMOS ICs can be detected.

In this paper, a built-in test circuit for an electrical interconnect test method is proposed to detect an open defect occurring at an interconnect between an IC and a printed circuit board. The test method is based on measuring the supply current of an inverter gate in the test circuit. A time-varying signal is provided to an interconnect as a test signal by the built-in test circuit. In this paper, the test circuit is evaluated by SPICE simulation and by experiments with a prototyping IC. The experimental results reveal that a hard open defect is detectable by the test method in addition to a resistive open defect and a capacitive open one at a test speed of 400 kHz.

In this paper, test time reduction for IDDQ testing is discussed. Although IDDQ testing is known to be effective to detect faults in CMOS circuit, test time of IDDQ testing is larger than that of logic testing since supply current is measured after a circuit is in its quiescent state. It is shown by simulation that test time of IDDQ test mostly depends on switching current. A procedure to modify test vectors and a procedure to arrange test vectors are presented for reducing the test time of IDDQ testing. A test sequence is modified such that switching current quickly disappears. The procedure utilizes a unit delay model to estimate the time of the last transition of logic value from L to H in a circuit. Experimental results for benchmark circuits show the effectiveness of the procedure.

When a feedback bridging fault occurs in a combinational circuit and it is activated, logical oscillation may occur in the circuit. In this paper, some electrical conditions are proposed to identify whether a feedback bridging fault occurs logical oscillation. Also, it is proposed how to estimate the oscillation frequency. They are based on piece linearlized models and do not require circuit simulation of large size of circuits. They are evaluated by some experiments. In the experiments, all of the feedback bridging faults occurring logical oscillation are identified. Also, oscillation frequencies larger than the ones obtained by SPICE simulation are derived by the proposed estimation method in the experiments. It promises us that the methods will be used for identifying such bridging faults and estimating the oscillation frequencies.

Open faults are difficult to test since the voltage at the floating line is unpredictable and depends on the voltage at the adjacent lines. The effect of open faults can be easily excited if a test pattern provides the opposite logic value to most of the adjacent lines. In this paper, we present a procedure to generate as high a quality test as possible. We define the test quality for evaluating the effect of adjacent lines by assigning an opposite logic value to the faulty line. In our proposed test generation method, we utilize the SAT-based ATPG method. We generate test patterns that propagate the faulty effect to primary outputs and assign logic values to adjacent lines opposite that of the faulty line. In order to estimate test quality for open faults, we define the excitation effectiveness Eeff. To reduce the test volume, we utilize the open fault simulation. We calculate the excitation effectiveness by open fault simulation in order to eliminate unnecessary test patterns. The experimental results for the benchmark circuits prove the effectiveness of our procedure.

In this paper, supply current testing for detecting open defects in CMOS circuits is discussed. It is known that open defects cause unpredictable faulty effects and are difficult to be detected. In our test method, an AC electric field is applied during testing. The voltage at a floating node caused by an open defect is varied by the applied electric field and then the defect can be detected. The test pattern generation procedure for open defects is proposed and is applied to benchmark circuits. The experimental results shows that the number of test vectors for opens are much smaller than that for stuck-at faults. The experimental evaluation for an LSI chip is also shown to present the feasibility of our test method.

A new state reduction method of incompletely specified sequential machines is proposed in this paper. The method is based on a genetic algorithm implementing a dormant mechanism. MCNC benchmark machines are simplified by using this method to evaluate the method. The experimental results show that machines of almost the same number of states as the minimum ones can be derived by this method.

In this paper, a test method is proposed to detect lead opens in CMOS LSIs. The test method is based on supply current which flows when test input vectors and AC electric field are provided from the outside of the ICs. Also, an application method of the test input vectors is proposed in this paper. It is shown experimentally that lead opens of SSIs and LSIs will be detected by providing each of the test input vectors per the period of AC electric field applied.

Small delay caused by a resistive open is difficult to test since circuit delay varies depending on various factors such as process variations and crosstalk even in fault-free circuits. We consider the problem of discriminating a resistive open by anomaly detection using delay distributions obtained by the effect of various input signals provided to adjacent lines. We examined the circuit delay in a fault-free circuit and a faulty circuit by applying electromagnetic simulator and circuit simulator for a line structure with adjacent lines under consideration of process variations. The effectiveness of the method that discriminates a resistive open is shown for the results obtained by the simulation.