James Chien-Mo Li

Testing for resistive opens and stuck opens

This paper studies the behavior of stuck and resistive open defects. The effects on test results of three test conditions (supply voltage, speed, temperature) as well as test patterns applied are evaluated. Diagnosis schemes for stuck and resistive opens are also presented. Five Murphy chips are diagnosed as having stuck open defects and one chip is diagnosed as having a resistive open defect. Their experimental data match our expectations for stuck opens and resistive opens.

Diagnosis of sequence-dependent chips

A technique capable of diagnosing single and multiple stuck-open and stuck-at faults is presented. Eleven sequence-dependent chips (test results depend on the order of test patterns) are diagnosed. Seven of them are diagnosed as having single stuck-open faults. Two of them are diagnosed as having multiple stuck-at and stuck-open faults.

Jump scan: a DFT technique for low power testing

This paper presents a Jump scan technique (or J-scan) for low power testing. The J-scan shifts two bits of scan data per clock cycle so the scan clock frequency is halved without increasing the test time. The experimental data show that the proposed technique effectively reduces the test power by two thirds compared with the traditional MUX scan. The presented technique requires very few changes in the existing MUX-scan design for testability methodology and needs no extra computation. The penalties are area overhead and speed degradation.

Survey of Scan Chain Diagnosis

Scan-based testing has proven to be a cost-effective method for achieving good test coverage in digital circuits. The Achilles heel in the application of scan-based testing is the integrity of the scan chains. The amount of die area consumed by scan elements, chain connections, and control circuitry varies with different designs. Typically, each scan cell in a scan chain has an index number. The cells in the chain are sequentially numbered from scan output to scan input, starting with 0. A chain pattern (sometimes called a flush pattern) is a pattern consisting of shift-in and shift-out operations without pulsing capture clocks. The purpose of chain patterns is to test scan chain integrity. A scan pattern (also known as a logic test pattern) is a pattern consisting of a shift-in operation, one or multiple capture clock cycles, and a shift-out operation. The purpose of scan patterns is to test system logic. The scan cells between the scan chain input and a scan cells scan input terminal are called the upstream cells of that scan cell. The scan cells between the scan chain output and a scan cells scan output terminal are called the downstream cells of that scan cell.

Diagnosis of resistive-open and stuck-open defects in digital CMOS ICs

A resistive-open defect is an imperfect circuit connection that can be modeled as a defect resistor between two circuit nodes that should be connected. A stuck-open (SOP) defect is a complete break (no current flow) between two circuit nodes that should be connected. Conventional single stuck-at fault diagnosis cannot precisely diagnose these two defects because the test results of defective chips depend on the sequence of test patterns. This paper presents precise diagnosis techniques for these two defects. The diagnosis techniques take the test-pattern sequence into account, and therefore, produce precise diagnosis results. Also, our diagnosis technique handles multiple faults of different fault models. The diagnosis techniques are validated by experimental results. Twelve SOP and one resistive-open chips are diagnosed out of a total of 459 defective chips.

A Secure Test Wrapper Design Against Internal and Boundary Scan Attacks for Embedded Cores

This paper presents a secure test wrapper (STW) design that is compatible with the IEEE 1500 standard. STW protects not only internal scan chains but also primary inputs and outputs, which may contain critical information (such as encryption keys) during the system operation. To reduce the STW area, flip-flops in the wrapper boundary cells also serve as the LFSR to generate the golden key. Experimental results on an AES core show that STW provides very high security at the price of only 5% area overhead with respect to the original IEEE 1500 test wrapper.

Testing for tunneling opens

A tunneling-open failure mode is proposed and carefully studied. A circuit with a tunneling open could pass at-speed Boolean tests but fail VLV testing or I/sub DDQ/ testing. Theoretical calculations as well as Boolean and I/sub DDQ/ experiments confirm the existence of tunneling opens. The Murphy experimental data show that seven out of nine VLV-only failure circuits can be explained by this failure mode. All these seven circuits survived 366 hours temperature burn-in. Finally, a cost effective screening strategy is proposed.

Diagnosis of multiple hold-time and setup-time faults in scan chains

This paper presents a diagnosis technique to locate hold-time (HT) faults and setup-time (ST) faults in scan chains. This technique achieves deterministic diagnosis results by applying thermometer scan input (TSI) patterns, which have only one rising or one falling transition. With TSI patterns, the diagnosis patterns can be easily generated by existing single stuck-at fault test pattern generators with few modifications. In addition to the first fault, this technique diagnoses remaining faults by applying thermometer scan input with padding (TSIP) patterns. For the benchmark circuits (up to 6.6 K scan cells), experiments show that the diagnosis resolutions are no worse than 15, even in the presence of multiple faults in a scan chain.

Testing of TSV-Induced Small Delay Faults for 3-D Integrated Circuits

Through silicon via (TSV) is a widely used interconnect technology in 3-D integrated circuits. This paper shows that defective TSVs can induce small delay faults in surrounding logic gates. We present simulation results of TSV-induced small delay fault (TSDF) because of mechanical stress or pinhole leakage. A test technique is proposed to detect TSDF using a physical-aware fault extractor and timing-aware automatic test pattern generation. This technique requires no DfT area overhead and no direct TSV probing. Experimental results on benchmark circuits show that test coverage can be improved by 22% and 10% for stress-induced and leakage-induced TSDF, respectively. In our results, the test length overheads of both TSDFs are <; 5%.

Simultaneous capture and shift power reduction test pattern generator for scan testing

An automatic test pattern generation (ATPG) technique, which simultaneously reduces capture and shift power during scan testing, is presented. This ATPG performs power reduction during dynamic test compaction so the test length overhead is very small. This low-power test generator implements several novel techniques, such as parity backtrace, confined propagation, dynamic controllability and post-fill test regeneration. The experimental data on ISCAS benchmark circuits show that the peak capture power and the peak shift power are reduced by 31% and 26%, respectively.