Dynamic random access memory having junction field effect transistor cell access device
A dynamic random access memory (DRAM) device can include a plurality of memory cells. Each memory cell can include a charge storing structure and an access device comprising an enhancement mode junction field effect transistor (JFET). The DRAM device can further include a plurality of sense amplifiers that each generates an output value in response to a signal received at respective sense amplifier inputs, and a plurality of bit lines, each bit line coupling a plurality of memory cells to at least one input of at least one of the sense amplifiers. A method can fabricate such DRAM devices.
1. A dynamic random access memory (DRAM) device, comprising:
a plurality of memory cells, each memory cell including an access junction field effect transistor (JFET) having at least a gate electrode and a drain electrode formed from a semiconductor layer and in physical contact with a semiconductor substrate; and
at least one sense amplifier coupled to selected of the memory cells, the sense amplifier including a sense bipolar junction transistor (BJT) having an emitter electrode formed from the semiconductor layer and in physical contact with the semiconductor substrate; wherein,
the sense BJT includes
a first base region comprising a first portion of the semiconductor substrate doped to one conductivity type,
a second base region comprising a second portion of the semiconductor substrate doped to the one conductivity type,
a lightly doped base region formed below the emitter electrode comprising a third portion of the semiconductor substrate doped to the one conductivity type,
a first base intermediate region disposed between the first base region and the lightly doped base region comprising a fourth portion of the substrate doped to the one conductivity type, and
a second base intermediate region disposed between the second base region and the lightly doped base region comprising a fifth portion of the substrate doped to the one conductivity type.
2. The DRAM device of claim 1 , further including:
a plurality of bit lines;
a plurality of select circuits, each comprising a JFET having a source-drain path coupled between one of the bit lines and at least one sense amplifier, and
the sense bipolar transistor of each sense amplifier has at least one terminal coupled to one of the bit lines by one of the select circuits.
3. The DRAM device of claim 1 , wherein:
the sense bipolar transistor of each sense amplifier is coupled to selected memory cells at its base terminal.
4. The DRAM device of claim 1 , further including:
the sense bipolar transistor of each sense amplifier is coupled to selected memory cells at its emitter terminal.
5. The DRAM device of claim 1 , wherein:
each access JFET further includes
a drain region below and in contact with the drain electrode comprising a first portion of the semiconductor substrate doped to one conductivity type,
a source region comprising a second portion of the semiconductor substrate doped to the one conductivity type,
a channel region formed below the gate electrode comprising a third portion of the semiconductor substrate doped to the one conductivity type,
a first link region disposed between the drain region and the channel region comprising a fourth portion of the substrate doped to the one conductivity type, and
a second link region disposed between the source region and the channel region comprising a fifth portion of the substrate doped to the one conductivity type, wherein
the source and drain regions have a higher dopant concentration than the first and second link regions, which have a higher dopant concentration than the channel region.