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Nov 25th, 2013
TSV stacked memory: a closer look
There is a lot of confusion among non memory experts as to how stacked memory technology with TSV is evolving. I-Micronews thought we should take …A closer look.
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DDR SDRAM (Double data rate synchronous dynamic random-access memory) when compared to  single data rate SDRAM, makes higher transfer rates possible by more strict control of the timing of the electrical data and clock signals. The name "double data rate" refers to the fact that a DDR SDRAM with a certain clock frequency achieves nearly twice the bandwidth of a SDR SDRAM running at the same clock frequency. For example, with data being transferred 64 bits at a time, DDR SDRAM gives a transfer rate of (memory bus clock rate) × 2 (for dual rate) × 64 (number of bits transferred) / 8 (number of bits/byte). Thus, with a bus frequency of 100 MHz, DDR SDRAM gives a maximum transfer rate of 1600 MB/s.
JEDEC released the first DDR SDRAM specifications (JESD79) in 2000.  DDR SDRAM modules for desktop computers are commonly called DIMMS.
Several variations exist depending on the intended application as shown below. GDDR (graphics) for graphics and LPDDR (low power) for the mobile space.

DDR memory by application

For those of you that are electrical engineers the differences between these DDR variations are shown below.

Differences in DDR architecture

Comparison of the required voltages and data transfer speeds for the various generations of DDR are shown below.

VDD vs data rate for DDR generations

Although all types of DRAMS are meeting their limits in terms of supply voltage, the demand for high-bandwidth memory keeps increasing. Thus memory companies looked at TSV based 3DIC solutions

Advantages of DRAM with TSV

- Higher density per area
- Shorter interconnection : lower power, faster flight time
- Higher bandwidth with wide I/O (for example  800 Mb/s/pin ×512 I/O ≈ 448 Gb/s/chip)

Again, these again separate into 3 types depending on application

TSV based memories for various microelectronic applications

Hynix indicates that for graphics HBM (high bandwidth memory) results in 65% increase in performance and a  40% decrease in power consumption (more).  

HBM vs DDR5 for graphics applications

Below we see the power comparison for a 16 Gb DDR3 DIMM vs a 8 chip 3D stack of 2GB DDR3 chips. We can see the 3D stack power consumption is much lower than the DDR3 DIMM and in fact nearly equivalent to an 8Gb DDR3 DIMM (more).

Comparison of power consumption for DDR3 DIMM vs DDR3 TSV stack

Lastly lets look at the memory option for several high volume applications. 

Memory options for high volume microelectronic applications



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