(158a) Engineering the Interplay Between Ion and Electron Transport for Low-Power Transistors and Memory

The interplay between ions and electrons governs the
performance of devices as ubiquitous as batteries, and processes as common as
the biochemistry essential for life. 
Our group uses ions to control electron and hole transport in
two-dimensional (2D) materials for the development of beyond-CMOS, low-power
transistors, and a new type of graphene-based flash
memory.  We demonstrate reconfigurable
p- and n-type doping of a 2D field effect transistor (FET) based on the transition
metal dichalcogenide (TMD), MoTe₂; the
ON/OFF ratio exceeds 10⁵ and the subthreshold
swing is 90 mV/decade (ACS Nano, Article ASAP, DOI: 10.1021/nn506521p).  These values are achieved by exploiting
the temperature-dependent relationship between ion and polymer mobility of the
electrolyte gate.  By doping the
channel p- or n-type and lowering the device temperature below the glass
transition temperature (T_g) of the
electrolyte, the ions are effectively "locked" into place with doping densities
exceeding 10¹³ cm^-2 for both electrons and holes.  The lock-in temperature is well below
room temperature (~220 K) for PEO-based electrolytes making this approach an
impractical gating strategy; however, our group has shown that the lock-in
temperature can be increased to room temperature by increasing the T_g of the polymer electrolyte.  The formation and relaxation dynamics associated
with p- and n-type doping can be described by a stretched exponential,
providing a way to quantify the temperature-dependent doping retention
time.  Field-driven ion transport is
modeled using COMSOL multiphysics.  This work highlights the application of
chemical engineering and polymer physics principles to the development of
beyond-CMOS nanoelectronics. 

This work was supported in part by the Center for Low Energy
Systems Technology (LEAST), one of six centers of STARnet,
a Semiconductor Research Corporation program sponsored by MARCO and DARPA.

Figure:  (a) Cross-sectional
schematic of electrolyte-gated MoTe₂ field effect transistor (FET)
(b) Transfer characteristics showing ~90 mV/decade subthreshold swing (c)
Normalized drain current versus time capturing the temperature-dependent
relaxation of the ions away from the channel surface (d) Temperature dependent
relaxation time from both experiments and modeling.