BEOL-Compatible 4F² Oscillator Using Vertical InGaAs Biristor for Highly Scalable Monolithic 3D Ising Solver

Ising solvers are important for efficiently addressing non-deterministic polynomial-time (NP)-hard combinatorial optimization problems (COPs), where scalability and compactness are crucial for practical applications. In this study, an experimental demonstration of an oscillator-based Ising solver employing a highly scalable 4F² InGaAs bi-stable resistor (biristor) is presented. It is first explored the oscillation behavior of the InGaAs biristor, establishing that classical Ising spins can be emulated using the sub-harmonic injection locking (SHIL) technique. Furthermore, capacitive and resistive coupling between two coupled InGaAs biristors is demonstrated, leading to out-of-phase and in-phase coupling, respectively. Employing this foundational technology, it is experimentally achieved a solution to the MaxCUT problem with the InGaAs biristor-based Ising solver, supplemented by simulation-based behavior evaluations. This emerging device architecture offers a viable pathway to surmount the scaling limitations faced by present hardware-based Ising solvers, representing a significant step forward in the development of efficient, scalable solutions for complex optimization challenges.