Ultra-Compact Phase-Change GeTe-Based Scalable mmWave Latching Crossbar Switch Matrices

This article presents millimeter-wave (mmWave) chalcogenide nonvolatile phase change material (PCM) germanium-telluride (GeTe)-based scalable switch matrices in a crossbar configuration. Two crossbar switch matrices in the form of
$2 \times 2$
and
$4 \times 4$
configurations are designed utilizing PCM four-port crossbar unit cells designed to have two states. The presented
$2 \times 2$
switch matrix utilizes a maximum of only two series PCM switches in any possible signal route, minimizing the insertion loss. A switch unit cell is optimized in terms of design and signal routing to improve the RF performance. The nonvolatile PCM switches consume no static dc power. The proposed switch matrices are fabricated in-house using an eight-layer custom microfabrication process. A design approach for scaling to higher order matrices is discussed, with an experimental demonstration of a
$4 \times 4$
switch matrix. Both
$2 \times 2$
and
$4 \times 4$
switch matrices are ultra-compact in size with the device area under 0.1 mm
²
for
$2 \times 2$
and less than 0.38 mm
²
for
$4 \times 4$
switch matrix. Over dc to 40 GHz, the fully integrated
$2 \times 2$
switch matrix exhibits a measured insertion loss less than 1.35 dB, a return loss better than 20 dB, and isolation higher than 24 dB. The
$4 \times 4$
switch matrix demonstrates a measured insertion loss of lower than 4.2 dB, a return loss better than 18 dB, and isolation better than 26 dB over the entire 40 GHz bandwidth. In addition, utilizing the scalability approach, two crossbar switch matrices of order
$4\times12$
and
$16\times16$
are also developed for dc/low-frequency switching applications.