Jwu-E Chen

Placement Optimization for Yield Improvement of Switched-Capacitor Analog Integrated Circuits

Capacitor mismatch can generally result from two sources of error: random mismatch and systematic mismatch. Random mismatch is caused by process variation, while systematic mismatch is mainly due to an asymmetrical layout and processing gradients. A common centroid structure may be used to reduce systematic mismatch errors, but not random mismatch errors. Based on the spatial correlation model, this paper formulates the placement optimization problem of analog circuits using switched-capacitor techniques. A placement with higher correlation coefficients of the unit capacitors results in a higher acceptance rate, or chip yield. This paper proposes a heuristic algorithm that quickly and automatically derives the placement of the unit capacitors with the highest, or near-highest, correlation coefficients for yield improvement. Results show that the resultant placement derived from the proposed algorithm achieves better yield improvement than that from a common centroid approach. The proposed heuristic algorithm can be applied for any arbitrary capacitor ratios, i.e., more than two capacitors.

Impact of Capacitance Correlation on Yield Enhancement of Mixed-Signal/Analog Integrated Circuits

Random fluctuations in process conditions change the physical properties of parameters on a chip. The correlation of device parameters depends on spatial locations. In general, the closer devices most likely have the similar parameter variation. The key performance of many analog circuits is directly related to accurate capacitance ratios. Parallel unit capacitances have a great effect on reducing ratio mismatch. This paper addresses the impact of capacitance correlation on the yield enhancement of mixed-signal/analog integrated circuits. The relationship between correlation and variation of capacitance ratio is also presented. Therefore, both mismatch and variation of capacitance ratio can be expressed in terms of capacitance correlation. Furthermore, both process variation and device mismatch are considered in the early design phase to reduce the design costs and speed up the time to market.

A Multilayer Data Copy Test Data Compression Scheme for Reducing Shifting-in Power for Multiple Scan Design

The random-like filling strategy pursuing high compression for todays popular test compression schemes introduces large test power. To achieve high compression in conjunction with reducing test power for multiple-scan-chain designs is even harder and very few works were dedicated to solve this problem. This paper proposes and demonstrates a multilayer data copy (MDC) scheme for test compression as well as test power reduction for multiple-scan-chain designs. The scheme utilizes a decoding buffer, which supports fast loading using previous loaded data, to achieve test data compression and test power reduction at the same time. The scheme can be applied automatic test pattern generation (ATPG)-independently or to be incorporated in an ATPG to generate highly compressible and power efficient test sets. Experiment results on benchmarks show that test sets generated by the scheme had large compression and power saving with only a small area design overhead.

A unified approach to detecting crosstalk faults of interconnects in deep sub-micron VLSI

The crosstalk fault effects in deep sub-micron VLSI, namely, glitches and the crosstalk-induced delay, are investigated. The origin of their occurrence, relationship and importance in circuit operation are elucidated. It is shown that the crosstalk-induced delay is only superposition of the induced glitch with the original signal delay on the affected victim line; and crosstalk-induced delay is more important in affecting the circuit performance, and should be considered in more details for testing. A scheme which is to detect both types of faults in a unified way by just detecting glitches is proposed and studied, considering the manufacture process variation. In this way, detection of crosstalk-induced faults becomes much easier.

A Unified Detection Scheme for Crosstalk Effects in Interconnection Bus

For very deep sub-micrometer VLSI, crosstalk becomes an important issue in affecting performance and signal integrity of the circuits. Two crosstalk fault effects, namely, glitch and crosstalk-induced delay, in the system-on-chip (SOC) interconnect bus are analyzed and a unified scheme to detect them is proposed and demonstrated in this paper. The crosstalk induced delay is found to be superposition of the induced glitch and the applied signal at the victim line, and this effect is more important in affecting the circuit performance. A pulse detector with an adjustable detection threshold is proposed to detect glitches and consequently the induced delay. Several issues affecting the yield of the proposed testing scheme are discussed and Monte Carlo simulations are conducted to show the feasibility of the scheme.

Multilevel Full-Chip Routing With Testability and Yield Enhancement

We propose a multilevel full-chip routing algorithm that improves testability and diagnosability, manufacturability, and signal integrity for yield enhancement. Two major issues are addressed. 1) The oscillation ring test (ORT) and its diagnosis scheme for interconnects based on the popular IEEE Standard 1500 are integrated into the multilevel routing framework to achieve testability enhancement. We augment the traditional multilevel framework of coarsening and uncoarsening by introducing a preprocessing stage that analyzes the interconnect structure for better resource estimation before the coarsening stage, and a final stage after uncoarsening that improves testability to achieve 100% interconnect fault coverage and maximal diagnosability. 2) We present a heuristic to reduce routing congestion to optimize the multiple-fault probability, chemical-mechanical polishing- and optical proximity correction-induced manufacturability, and crosstalk effects, for yield improvement. Experimental results on the Microelectronics Center for North Carolina benchmark circuits show that the proposed ORT method achieves 100% fault coverage and the optimal diagnosis resolution for interconnects. Further, the multilevel routing algorithm effectively balances the routing density to achieve 100% routing completion.

Yield evaluation of analog placement with arbitrary capacitor ratio

Capacitance mismatch can be generally attributed two sources of errors: random mismatch and systematic mismatch. Random mismatch is caused by the process variation, while systematic mismatch is mainly due to asymmetrical layout and processing gradients. Common centroid structure may reduce the systematic mismatch, but not the random mismatch. Based on spatial correlation model, this study derives the relationship among correlation, mismatch, and variation of capacitance ratio. Results show that the placement of unit capacitance array with higher correlation results in lower mismatch and lower variation of capacitance ratio. For any arbitrary capacitance ratio, i.e., more than two capacitors, if the summation of correlation coefficients for all capacitance pairs is defined as ¿index¿, the placement with higher index results in higher yield, where the yield is defined as the ratio of the acceptable designs over the sample size. In other words, one can find a near-optimal placement which has better yield by using the simple calculation of index, instead of the complicated circuit simulations.

Optimal common-centroid-based unit capacitor placements for yield enhancement of switched-capacitor circuits

Yield is defined as the probability that the circuit under consideration meets with the design specification within the tolerance. Placement with higher correlation coefficients has fewer mismatches and lower variation of capacitor ratio, thus achieving higher yield performance. This study presents a new optimization criterion that quickly determines if the placement is optimal. The optimization criterion leads to the development of the concepts of C-entries and partitioned subarrays which can significantly reduce the searching space for finding the optimal/near-optimal placements on a sufficiently large array size.

Yield improvement by test error cancellation

While an integrated circuit is fabricated and tested, errors may be introduced during manufacturing and testing processes. An IC development flow driven by yield improvement, which includes two stages of testing evaluations, called engineering and production runs, for test error classification and cancellation, is proposed in this paper. Six error-syndromes including mask, process, scrape, probe-card, probe-pin, and test-specification errors are classified by wafer map analysis. Test Errors can be canceled by either re-testing or re-adjusting the test-specification derived from designer/application-engineer and test engineer. An ASIC CMOS chip is used to validate the proposed testing process and the yield of this product is improved up to 16% in production line.

To verify manufacturing yield by testing

The effect of test errors should be cancelled while before test yield is used to analyze the manufacturing yield. Test errors can be alleviated from engineering run and production run stages. One of the more difficult aspect of yield modeling is the fact that defect density is generally not constant with time. In this paper, we study the flow of defect monitor used in production test. Based on the yield data obtained from engineering stage, the upper and lower bounds of chip yield are calculated after determining the variance of defect density and clustering parameter. The yield bound/distribution is used to diagnose the results after wafer sort while in production. One ASIC product is used to validate this yield analysis procedure. This work can assist the ASIC design center to determine a manufacturing laboratory beginning the design and to control the chip area in the period of circuit design.<<ETX>>