Toshio Takeshima

A 30-ns 64-Mb DRAM with built-in self-test and self-repair function

A 64 Mw*1 b/16 Mw*4 b DRAM with 30-ns access time which uses a double-metal layer and 0.4- mu m CMOS technology is reported. The external power supply is 3 V, while memory cell arrays operate at 2.2 V. Key circuits for the 64-Mb DRAM are (1) a latched-sense, shared-sense circuit with open bit-line read-out and folded bit-line rewrite operations (LOF) to reduce inter-bit-line coupling noise, (2) alternatively activated and separately end-located word drivers and X decoders to reduce word-line selection delay, and (3) built-in self test and repair circuits using spare memory cells to reduce test costs and increase chip reliability. >

A 30-ns 256-Mb DRAM with a multidivided array structure

A 256-Mb DRAM with a multidivided array structure has been developed and fabricated with 0.25- mu m CMOS technology. It features 30-ns access time, 16-b I/Os, and a 35-mA operating current at a 60-ns cycle time. Three key circuit technologies were used in its design: a partial cell array activation scheme for reducing power-line voltage bounce and operating current, a selective pull-up data-line architecture to increase I/O width and reduce power dissipation, and a time-sharing refresh scheme to maintain the conventional refresh period without reducing operational margin. Memory cell size was 0.72 mu m/sup 2/. Use of the trench isolated cell transistor and the HSG cylindrical stacked capacitor cells helped reduce chip size to 333 mm/sup 2/. >

A BIST scheme using microprogram ROM for large capacity memories

A practical microprogram ROM BIST (built-in self-test) scheme suitable for LSI memories is proposed. This BIST can be used to install N-pattern and N/sup 2/-pattern test procedures, using BIST circuits with 12-word*10-b and 16-word*16-b ROMs, respectively. As a practical test procedure, a data retention test, in which BIST circuits with an 8-word*11-b ROM were used, was investigated. BIST circuit area overheads for the above three test patterns for 16-Mb DRAMs are less than 1%, 2%, and 1.5%, respectively. A testing method for the BIST circuits themselves, with no special BIST circuit overhead, is also proposed for more practical applications. The measured operational margin for a 16-Mb DRAM using the BIST showed a good agreement with that using an LSI tester.<<ETX>>

A 5 ns 1 Mb ECL BiCMOS SRAM

A 1 M-word*1-b emitter-coupled-logic (ECL) SRAM in 0.8- mu m BiCMOS technology that achieves 5-ns access time using (1) wired-OR predecoders, (2) ECL CMOS level converters with partial address decoding, and (3) sensing with small differential voltage swing on long read bus lines is described. The memory cell array is divided into two 512 K-cell subarrays. Each subarray consists of 16 32-kb arrays, each of which is organized into 256 rows and 128 columns. An X-decoder is located between a pair of 32-kb arrays. Address input signals are received by an ECL address buffer. The first circuit for address decoding is a wired-OR predecoder, which does the predecoding and predecoded signal line driving. Predecoded address signals with about 1.2-V voltage swing drive 16.5-mm predecoded lines between two 512-kb subarrays and are received by partial-decoding level converters at corresponding 32-kb arrays.<<ETX>>

A 98 mm/sup 2/ die size 3.3-V 64-Mb flash memory with FN-NOR type four-level cell

In order to realize high-capacity and low-cost flash memory, we have developed a 64-Mb flash memory with multilevel cell operation scheme. The 64-Mb flash memory has been achieved in a 98 mm/sup 2/ die size by using four-level per cell operation scheme, NOR type cell array, and 0.4-/spl mu/m CMOS technology. Using an FN type program/erase cell allows a single 3.3 V supply voltage. In order to establish fast programming operation using Fowler-Nordheim (FN)-NOR type memory cell, we have developed a highly parallel multilevel programming technology. The drain voltage controlled multilevel programming (DCMP) scheme, the parallel multilevel verify (PMV) circuit, and the compact multilevel sense-amplifier (CMS) have been implemented to achieve 128 b parallel programming and 6.3 /spl mu/s/Byte programming speed.

A 55-ns 16-Mb DRAM with built-in self-test function using microprogram ROM

A single 5-V power supply 16-Mb dynamic random-access memory (DRAM) has been developed using high-speed latched sensing and a built-in self-test (BIST) function with a microprogrammed ROM, in which automatic test pattern generation procedures were stored by microcoded programs. The chip was designed using a double-level Al wiring, 0.55- mu m CMOS technology. As a result, a 16-Mb CMOS DRAM with 55-ns typical access time and 130-mm/sup 2/ chip area was attained by implementing 4.05- mu m/sup 2/ storage cells. The installed ROM was composed of 18 words*10 b, where the marching test and checkerboard scan write/read test procedures were stored, resulting in successful self-test operation. As the BIST circuit occupies 1 mm/sup 2/ and the area overhead is about 1%, it proves to be promising for large-scale DRAMs. >

A 98 mm/sup 2/ 3.3 V 64 Mb flash memory with FN-NOR type 4-level cell

A 64 Mb flash memory has a multi-level cell and 64-memory-cell parallel programming. 98 mm/sup 2/ die uses 0.4 /spl mu/m CMOS and 4-levels (2b) per cell. 3.3 V operation and 6.3 /spl mu/s/B programming are achieved by using a Fowler-Nordheim (FN) NOR memory cell. Drain-voltage controlled multilevel programming (DCMP) is the key technology for simultaneous multi-level programming in the chip. To implement DCMP, a parallel multi-level verify (PMV) circuit and the compact multi-level sense amplifier (CMS), which enable a 64-memory-cells parallel programming operation (program/program verify), are used.

A 3.3 V single-power-supply 64 Mb flash memory with dynamic bit-line latch (DBL) programming scheme

A 3.3 V single-power-supply 64 Mb (4M words x 16b) flash memory with a dynamic bit-line latch (DBL) programming has 50 ns access time and 256 b erase/programming unit-capacity using hierarchical word- and bit-line structures and DBL programming. This memory is fabricated using a 0.4 /spl mu/m-design-rule, double-layer-aluminum, triple-layer-polysilicon, twin-well CMOS technology. To reduce operating voltage, a high-capacitive-coupling ratio (HiCR) cell with high coupling ratio between the control gate and the floating gate is used.<<ETX>>

A 55 ns 16 Mb DRAM

The authors describe a 16-Mb CMOS DRAM (dynamic RAM) with 55-ns access time and 130-mm/sup 2/ chip area. It features a high-speed latched sensing (LS) scheme and a built-in self-test (BIST) function with a microprogrammable ROM in which automatic test pattern generation procedures are stored by microcoded programs. To achieve 55-ns access time, the DRAM combines the LS scheme with conventional double-Al-layer wiring and 5-V peripheral circuits. The bit-line sense circuits, driven at 3.3 V from an internal voltage converter to ensure 0.6 mu m MOS memory cell reliability, are shown. Both sensing speed and signal voltage are lower at 3.3 V operation than at 5 V operation. However, the LS scheme compensates for these drawbacks and achieves fast access time and high sensitivity. Operational waveforms for 55-ns row-address-strobe access time for a typical chip under normal conditions are shown, and chip characteristics are summarized.<<ETX>>

Quasi-worst-condition built-in-self-test scheme for 4-Mb loadless CMOS four-transistor SRAM macro

We have developed a quasi-worst-condition Built-In-Self-Test (BIST) scheme capable of detecting defective cells. The effectiveness of the BIST, which is conducted at the time of power supply injection, is independent of ambient temperature. Measurement results indicate that defective cells detected in a wafer functional test in worst condition would also be detected with our newly developed BIST.