Double-Gate Junctionless 1T DRAM With Physical Barriers for Retention Improvement
Md. Hasan Raza Ansari, Nupur Navlakha, Jae Yoon Lee, Seongjae Cho
Abstract
In this article, a double-gate (DG) junction-less (JL) transistor with physical barriers is proposed for one-transistor dynamic random-access memory (1T DRAM) application. In this topology, the holes are stored in the region blocked by physical barriers constructed by oxides underneath the source and drain regions rather than a potential well formed by n+-p-n+ as in the conventional structures. The proposed topology achieves an elongated retention time (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ret</sub> ) with larger physical barrier thickness (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oxPB</sub> ) and wider barrier offset length (LBO) due to a reduction in band-to-band tunneling (BTBT) (during hold “0”) and recombination (during hold “1”). Maximum retention times of ~2.5 s and ~33 ms have been achieved for channel doping of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> at 27 °C and 85 °C, respectively, with gate length (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ) of 100 nm at small drain bias (VDS) of 1 V during write “1.” Results demonstrate a better gate length scalability and a retention time of ~4 ms at L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> of 15 nm with thinner Si channel thickness under the gate (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Si</sub> ) and thicker T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oxPB</sub> . In addition, the effect of temperature on retention time has been analyzed. With optimized T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oxPB</sub> at L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> = 100 nm, the retention time decreases due to thermal generation and recombination from ~2.5 s at 27 °C to ~3 ms at 125 °C.