  A voltage-controlled topological-spin switch (vTOPSS) that uses a hybrid
topological insulator-magnetic insulator multiferroic is presented that can
implement Boolean logic operations with sub-10 aJ energy-per-bit and
energy-delay product on the order of $10^{-27}$ Js. The device uses a
topological insulator (TI), which has the highest efficiency of conversion of
electric field to spin torque yet observed at room temperature, and a
low-moment magnetic insulator (MI) that can respond rapidly to a given spin
torque. We present the theory of operation of vTOPSS, develop analytic models
of its performance metrics, elucidate performance scaling with dimensions and
voltage, and benchmark vTOPSS against existing spin-based and CMOS devices.
Compared to existing spin-based devices, such as all-spin logic and charge-spin
logic, vTOPSS offers 100$\times$ lower energy dissipation and (40-100)$\times$
lower energy-delay product. With experimental advances and improved material
properties, we show that the energy-delay product of vTOPSS can be lowered to
$10^{-29}$ Js, competitive against existing CMOS technology. Finally, we
establish that interconnect issues that dominate the performance in CMOS logic
are relatively less significant for vTOPSS, implying that highly resistive
materials can indeed be used to interconnect vTOPSS devices.
