Due to its capability of parallel search, content addressable memory (CAM) has been widely used on the applications requiring high-speed data search. In recent years, the architectures and design techniques for CAM have been consistently evolving. However, the incoming testing issues for those newly evolved CAM designs are not fully discussed. In this paper, we investigate the testing issues for a new 28nm quaternary CAM, which provides the additional fourth state compared to a conventional ternary CAM and utilizes a charge-sharing sensing scheme for reducing its search power consumption. We first identify the new fault models for this quaternary CAM that are not covered in the conventional CAM testing based on the simulation result, and derive the corresponding test algorithm for those new fault models. The effectiveness of the proposed test algorithm is then validated by the testing result of 7200 28nm sample chips covering different process corners with the help of a newly designed command-based memory BIST.

The recent research works of dual-port SRAM have focused on developing new write-assist techniques to suppress the potential inter-port write disturbance under low operating voltage and high process variation. However, the testing related issues induced by those newly proposed write-assist techniques have not been discussed yet in the previous literatures. In this paper, we first implemented a new write-assist dual-port SRAM proposed in [10] by using a 28nm LP process and then discussed the faulty behavior of injecting different resistive-open defects into both the SRAM cell and write-assist circuit. Next, we developed new test methods to detect the hard-to-detect resistive-open defects and proposed a corresponding March-like algorithm that covers a widely used March C- as well as the proposed test methods. Last, the required DfT for the proposed test methods was also discussed.

Due to the increasing demand of an extra-low-power system, a great amount of research effort has been spent in the past to develop an effective and economic subthreshold SRAM design. However, the test methods regarding those newly developed subthreshold SRAM designs have not yet been fully discussed. In this paper, we first categorize the subthreshold SRAM designs into three types, study the faulty behavior of open defects and address decoders faults on each type of designs, and then identify the faults which may not be covered by a traditional SRAM test method. We will also discuss the impact of open defects and threshold-voltage mismatch on sense amplifiers under subthreshold operations. A discussion about the temperature at test is also provided.

This paper presents a novel memory test algorithm, named alternate hammering test, to detect the pairwise word-line hammering faults for application-specific DRAMs. Unlike previous hammering tests, which require excessively long test time, the alternate hammering test is designed scalable to industrial DRAM arrays by considering the array layout for potential fault sites and the highest DRAM-access frequency in real system applications. The effectiveness and efficiency of the proposed alternate hammering test are validated through the test application to an eDRAM macro embedded in a storage-application SoC.

The embedded-DRAM (eDRAM) testing mixes up the techniques used for DRAM testing and SRAM testing since an eDRAM core combines DRAM cells with an SRAM interface (the so-called 1T-SRAM architecture). In this paper, we first present our test algorithm for eDRAM testing. A theoretical analysis to the leakage mechanisms of a switch transistor is also provided, based on that we can test the eDRAM at a higher temperature to reduce the total test time and maintain the same retention-fault coverage. Finally, we propose a mathematical model to estimate the defect level caused by wear-out defects under the use of error-correction-code circuitry, which is a special function used in eDRAMs compared to commodity DRAMs. The experimental results are collected based on 1-lot wafers with an 16 Mb eDRAM core.

With the advent of deep-submicrometer VLSI technology, the capacity and performance of semiconductor memory chips is increasing drastically. This advantage also makes it harder to maintain good yield. Diagnostics and redundancy repair methodologies thus are getting more and more important for memories, including embedded ones that are popular in system chips. In this paper, we propose an efficient memory diagnosis and repair scheme based on fail-pattern identification. The proposed diagnosis scheme can distinguish among row, column, and word faults, and subsequently apply the Huffman compression method for fault syndrome compression. This approach reduces the amount of data that need to be transmitted from the chip under test to the automatic test equipment (ATE) without losing fault information. It also simplifies the analysis that has to be performed on the ATE. The proposed redundancy repair scheme is assisted by fail-pattern identification approach and a flexible redundancy structure. The area overhead for our built-in self-repair (BISR) design is reasonable. Our repair scheme uses less redundancy than other redundancy schemes under the same repair rate requirement. Experimental results show that the area overhead of the BISR design is only 4.1% for an 8 K × 64 memory and is in inverse proportion to the memory size.

Due to the increasing demand of an extra-low-power system, a great amount of research effort has been spent in the past to develop an effective and economic subthreshold-SRAM design. However, the test methods regarding those newly developed subthreshold-SRAM designs have not yet been fully discussed. In this paper, we first categorize the subthreshold-SRAM designs into three types, study the faulty behavior of different open defects for each type of designs, and then identify the faults which may or may not be covered by a traditional SRAM test method. For those hard-to-detect faults, we will further discuss the corresponding test method according to different each type of subthreshold-SRAM designs. At last, a discussion about the temperature at test will also be provided.

In this paper, we compare embedded-DRAM (eDRAM) testing to both SRAM testing and commodity-DRAM testing, since an eDRAM macro uses DRAM cells with an SRAM interface. We first start from an standard SRAM test algorithm and discuss the faults which are not covered in the SRAM testing but should be considered in the DRAM testing. Then we study the behavior of those faults and the tests which can detect them. Also, we discuss how likely each modeled fault may occur on eDRAMs and commodity DRAMs, respectively.

The embedded-DRAM testing mixes up the techniques used for DRAM testing and SRAM testing since an embedded-DRAM core combines DRAM cells with an SRAM interface (the so-called 1T-SRAM architecture). In this paper, we first present our test algorithm for embedded-DRAM testing. A theoretical analysis to the leakage mechanisms of a switch transistor is also provided, based on that we can test the embedded-DRAM at a higher temperature to reduce the total test time and maintain the same retention-fault coverage. The experimental results are collected based on 1-lot wafers with an 16Mb embedded DRAM core.

This brief presents a built-in self-repair (BISR) scheme for semiconductor memories with two-dimensional (2-D) redundancy structures, i.e., spare rows and spare columns. The BISR design is composed of a built-in self-test module and a built-in redundancy analysis (BIRA) module. The BIRA module executes the proposed RA algorithm for RAM with a 2-D redundancy structure. The BIRA module also serves as the reconfiguration unit in the normal mode. Experimental results show that a high repair rate (i.e., the ratio of the number of repaired memories to the number of defective memories) is achieved with the BISR scheme. The BISR circuit has a low area overhead-about 4.6% for an 8 K /spl times/ 64 SRAM.

With the advent of deep submicron technology and system-on-chip (SOC) design methodology, we are seeing on-chip memory cores to represent a growing percentage of the chip area. The yield of an SOC is usually dominated by the memory yield, so the improvement of memory yield is crucial in SOC development. In this work, we propose a built-in self-repair (BISR) scheme for memory yield improving. The novelty of our approach is that we can identify the fail patterns so that appropriate spare elements (e.g., spare rows, columns, words, or blocks) can be allocated to repair the defective memory. Some BISR methods are discussed and compared. We select the scheme that uses fewer spare elements than others given the same repair rate. The area overhead of the BISR scheme is only 2.2% for an 8K/spl times/64 memory.

Embedded flash memory has been widely used in applications that require non-volatile on-chip storage elements. However, test and diagnostics of flash memories needs further investigation so that the overall cost of the products can be reduced. This paper presents the challenges and issues for test and diagnostics of flash memories, based on our recent experiences. We also suggest improvement of the test and diagnosis flow, including design-for-testability (DFT) using built-in self-test (BIST), built-in self-repair (BISR), and failure analysis. In addition, we present a configurable flash memory tester using FPGA for low-cost testing and diagnostics. Experimental results on industrial flash chips justify the effectiveness of our test and diagnostics system.

With the advent of system-on-chip (SOC), the demand for embedded memory cores increases rapidly. The magnetic random access memory (MRAM) is considered one of the potential candidates that replace current on-chip memories (RAM, EEPROM, and flash memory) in the future. The MRAM has a high speed and does not need high supply voltage for read/write operations, so it has the advantages of RAM and flash memory, making it a potentially good choice for SOC. The testing of MRAM, however, has not been fully investigated. In this work we classify and analyze the MRAM defects and their behavior, and propose its fault models. We have built a SPICE model of MRAM cell and performed defect injection and simulation of a real MRAM circuit. The circuit has been implemented and fabricated with a novel 0.18 m technology. The simulation results regarding the correlation between the defects and conventional fault models show that most of the defects can be covered by the stuck-at fault model. The test data based on the fabricated chips show that the stuck-at faults do cover most of the defects on the chips. However, from the experiment we also have identified two new faults, i.e., the Multi-Victims fault and Kink fault.

Fault analysis is an important step in establishing detailed fault models or subsequent diagnostics and debugging of a semiconductor memory product. We have performed defect injection in the memory cell array of an industrial SRAM circuit and analyzed the faulty behavior with respect to each defect injected. We found that although some of the defects can be mapped to existing fault models, there are many defects that result in unmodeled faults. Moreover, a defect may exhibit a different faulty behavior at a different location in the cell array. The voltage and temperature parameters can also change the faulty behavior. The simulation results show that almost all open and short defects lead to stuck-at faults, transition faults, and data retention faults.

We propose an embedded processor-based built-in self-repair (BISR) design for embedded memories. In the proposed design we reuse the embedded processor that can be found on almost every system-on-chip (SOC) product, in addition to many distinct features. By reusing the embedded processor, the controller and redundancy analysis circuit of a typical BISR design can be removed. Also, the test algorithm and redundancy analysis/allocation algorithm are easily programmable, greatly increasing the design flexibility. We also have developed a memory wrapper that allows at-speed testing of the memory cores. The area overhead of the proposed BISR scheme is low, since only the memory wrapper needs to be realized explicitly. Our experiments show that the BISR area overhead for a typical 8 K/spl times/32 SRAM is lower than 1%.

Embedded memories are among the most widely used cores in current system-on-chip (SOC) implementations. Memory cores usually occupy a significant portion of the chip area, and dominate the manufacturing yield of the chip. Efficient yield-enhancement techniques for embedded memories thus are important for SOC. In this paper we present a built-in self-repair (BISR) scheme for semiconductor memories with 2-D redundancy structures. The BISR design is composed of a built-in self-test (BIST) module and a built-in redundancy analysis (BIRA) module. Our BIST circuit supports three test modes: the 1) main memory testing, 2) spare memory testing, and 3) repair modes. The BIRA module executes the proposed redundancy analysis (RA) algorithm for RAM with a 2-D redundancy structure, i.e., spare rows and spare columns. The BIRA module also serves as the reconfiguration (address remapping) unit in the normal mode. Experimental results show that a high repair rate (i.e., the ratio of the number of repaired memories to the number of defective memories) is achieved with the proposed RA algorithm and BISR scheme. The BISR circuit has a low area overhead—about 4.6 % for an 8K¢64 SRAM.