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SDRAM cross section view: stack vs. trench capacitor concepts

Technologically two DRAM concepts dominated the market till 2009:

  1. Stack capacitor concept (see a cross section in Figure 1)
  2. Trench capacitor concept (see Figure 2);

The last microelectronic companies which produced, but not producing anymore, DRAM chips based on the trench capacitor concept were Infineon Technologies, namely its daughter company Qimonda, Inotera Memories, Nanya Technologies and Winbond. The “rest of the DRAM world” (Samsung, Micron, Elpida etc.) produced and are still producing DRAMs based on the stack capacitor concept.

The difference between the trench and stack concepts is actually relatively simple. In the case of the trench concept the capacitor of the elementary DRAM cell

is made by a trench in the single crystalline silicon substrate, i.e. the capacitor is buried in the substrate and it is bellow the transistor. On the other hand, the stack concept has the capacitor above the transistor and is made in a deposited amorphous oxide.

SDRAM cross section view: stack capacitor concept

Figure 1. A cross section view of a DRAM chip based on the stack capacitor concept; a) The stack capacitor; b) The transistor is bellow the stack capacitor;

 

SDRAM cross section view: Tranch capacitor concept

Figure 2. A cross section view of a DRAM chip based on the trench capacitor concept; a) A DRAM DIMM used in every computer; b) The schematic view of the elementary DRAM cell; c) DRAM cross section at the nanometer scale;  d) The transistor - one of the main two parts of a DRAM cell; e) Trench capacitor is bellow the transistor and is the second part of a DRAM cell; f) shows how the charge if flowing physically in a DRAM cell;