Woo-seop Kim

8 Gb 3-D DDR3 DRAM Using Through-Silicon-Via Technology

An 8 Gb 4-stack 3-D DDR3 DRAM with through-Si-via is presented which overcomes the limits of conventional modules. A master-slave architecture is proposed which decreases the standby and active power by 50 and 25%, respectively. It also increases the I/O speed to > 1600 Mb/s for 4 rank/module and 2 module/channel case since the master isolates all chip I/O loadings from the channel. Statistical analysis shows that the proposed TSV check and repair scheme can increase the assembly yield up to 98%. By providing extra VDD/VSS edge pads, power noise is reduced to < 100 mV even if all 4 ranks are refreshed every clock cycle consecutively.

A 3.6 Gb/s/pin simultaneous bidirectional (SBD) I/O interface for high-speed DRAM

A point-to-point I/O interface for high-speed DRAM is described. The interface utilizes simultaneous bidirectional signaling that enables transmitting/receiving data through a line at the same time. The test scheme is implemented in 0.10 /spl mu/m DRAM process. It achieves 3.6 Gb/s/pin in SBD mode and an I/O cell consumes 35 mW.

A 31 ns Random Cycle VCAT-Based 4F

A functional 4F2 DRAM was implemented based on the technology combination of stack capacitor and surrounding-gate vertical channel access transistor (VCAT). A high performance VCAT has been developed showing excellent Ion-Ioff characteristics with more than twice turn-on current compared with the conventional recessed channel access transistor (RCAT). A new design methodology has been applied to accommodate 4F2 cell array, achieving both high performance and manufacturability. Especially, core block restructuring, word line (WL) strapping and hybrid bit line (BL) sense-amplifier (SA) scheme play an important role for enhancing AC performance and cell efficiency. A 50 Mb test chip was fabricated by 80 nm design rule and the measured random cycle time (tRC) and read latency (tRCD) are 31 ns and 8 ns, respectively. The median retention time for 88 Kb sample array is about 30 s at 90°C under dynamic operations. The core array size is reduced by 29% compared with conventional 6F2 DRAM.

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Most DRAM interfaces such as GDDR5 and DDR3 use parallel single-ended signaling due to pin-count restriction and backward compatibility. Notwithstanding poor signal and power integrity issues, GDDR5 speed reached beyond 5Gb/s in recent years by utilizing data bus inversion, error-detection coding, data training and channel equalization [1–3]. However, channel crosstalk is becoming a major barrier to further speed improvement. A common solution for channel crosstalk reduction at the system level is to use a shielding line or wide spacing between signal lines, but increasing the number of layers in a chip package and PCB increase system cost. To remove the shielding lines and increase speed, this paper presents a channel crosstalk equalizer with programmable signal ordering capability for the DRAM transmitter. In addition, this paper addresses tri-mode clocking to reduce the system jitter for better timing margin: PLL off, LC-PLL and injection-locked oscillator.

DRAM With Manufacturability and Enhanced Cell Efficiency

This paper presents a simultaneous bi-directional (SBD) 4-level I/O interface for high-speed DRAMs. The data rate of 4 Gb/s/pin was demonstrated using a 500-MHz clock generator and a full CMOS rail-to-rail power swing. The power consumed by the I/O circuit was measured to be 28 mW/pin, when connected to a 10-pF load, at a 1.8-V supply voltage. The transmitter uses a 4-level push-pull linear output driver and a 4-level automatic impedance controller, achieving the reduction of driver currents and the voltage margin as large as 200 mV. The receiver employs a hierarchical sampling scheme, wherein a differential amplifier selects three out of six reference voltage levels. This scheme ensures minimized sampling power and a wide common-mode sampling range. The 6-level reference voltage for sampling is generated by the combination of the transmitter replica. The proposed I/O interface circuits are fabricated using a 0.10-/spl mu/m, 2-metal layers DRAM process, and the active area is 330 /spl times/ 66 /spl mu/m/sup 2/. It exhibits 200 mV /spl times/ 690 ps eye windows on the given channel with a 1.8-V supply voltage.

A 40nm 2Gb 7Gb/s/pin GDDR5 SDRAM with a programmable DQ ordering crosstalk equalizer and adjustable clock-tracking BW

This paper proposes a deca-data rate clocking scheme and relevant I/O circuit techniques for a multi-Gb/s/pin memory interface. A deca-data rate scheme transmits 10 bits in one external clock cycle to transfer an error control code along with original data seamlessly without a timing bubble. A 288 Mb SDRAM has been designed using the proposed scheme combined with fast cycling core techniques to have both high I/O bandwidth and fast random cycling. Measured results show that the chip exhibits per-pin data rate of 8 Gb/s and row cycle time of 9.6 ns

A 4-Gb/s/pin low-power memory I/O interface using 4-level simultaneous bi-directional signaling

A 7Gb/s single ended transceiver with low jitter and ISI is implemented in 40nm DRAM process. DRAM optimized LC PLL achieves inductor Q of 3.86 and results in random jitter of 670fs rms. A clock tree regulator with closed loop replica path reduces low as well as high frequency noise. RX 2-tap hybrid DFE combining sampling and integration methods reduces power and area by 37% and 24%, compared to the integrating DFE. Moreover, on-chip de-emphasis circuit in TX multiplexer reduces ISI of both on and off chip.

An 8 Gb/s/pin 9.6 ns Row-Cycle 288 Mb Deca-Data Rate SDRAM With an I/O Error Detection Scheme

A 1-Gbit DRAM with 5.8-Gb/s/pin unidirectional differential I/Os was implemented by 70 nm DRAM process and a main memory module with dual in-line memory module was assembled. The implemented DRAM chips have control methods for core noise injection and a cyclic redundancy check (CRC) generator for outer-data inner-command architecture. Measurements for bit error rate and jitter performance of the transmitter was performed on an electrical test board which emulates the real memory systems environment. Also, the effect on power noise was analyzed from the DRAM chips with three class values of power decoupling capacitance for the peripheral part. The results show that no additional coding for the differential I/O protection in DRAM, like CRC, is required up to 5.8-Gb/s/pin operation.

A 40nm 7Gb/s/pin single-ended transceiver with jitter and ISI reduction techniques for high-speed DRAM interface

A 5.8 Gb/s/pin DRAM with unidirectional differential I/Os and 1 Gbit memory core was designed and 23.2 GB/s memory module was assembled. Tx BER measurement on an electrical test board similar to real memory sub-systempsilas environment was performed and the results show that no additional coding for the differential I/O protection, like CRC, seems to be required up to 5.8 Gb/s/pin operation. Also, an efficient timing usage method using matched path for a possible implementation of CRC computation in ODIC architecture was proposed.

BER Measurement of a 5.8-Gb/s/pin Unidirectional Differential I/O for DRAM Application With DIMM Channel

This paper presents a high-speed LVDS I/O interface for mobile DRAMs. A data rate of 6Gbps/pin and a transmit-jitter of 57.31ps pk-pk were demonstrated, in which an 800MHz clock and a 200mV swing were used. The power consumption by I/O circuit is 6.2mW/pin when a 10pf load is connected to the I/O, and output supply voltage is 1.2V. The proposed mobile DRAM has 6 data pins and 4 address/command pins for a multi-chip package (MCP). The transmitter uses a feed-back LVDS output driver and a common-mode feed-back controller achieving the reduction of driver currents and the constant common-mode as half voltage level. To achieve a low-transmit jitter, we use a driver with a double step pre-emphasis. The receiver employs a shared preamplifier scheme, which ensures transmit power reduction. The proposed DRAM with LVDS I/O was fabricated using an 80-nm DRAM process. It exhibits 161.1mV times 150ps rms eye-windows on the given channel