Fabrication of Submicrometer InGaAs/AlAs Resonant Tunneling Diode Using a Trilayer Soft Reflow Technique With Excellent Scalability

A trilayer soft reflow fabrication method using solvent vapor that resulted in a submicrometer resonant tunneling diode (RTD) is reported in detail. The processing steps are simple, time efficient and are all based on conventional i-line photolithography. The trilayer soft reflow technique is able to shrink the emitter lateral width from 1 down to 0.35 μm (65% reduction) using a solvent at a very low temperature (<;50 °C). Studies of device´s peak current density (J_P) suggest that excellent scalability is achieved as the emitter area reduces from ~29 down to ~0.5 μm² with no significant increase in peak voltage (V_P) due to high series resistance normally associated with submicrometer dimensions. The valley current (I_V ), however, increases due to side-wall damage introduced by the reactive ion etching (RIE) process. As a result, the peak-to-valley-current ratio decreases from 5.0 (6.3) to 3.8 (4.1) in forward (reverse) direction as the emitter area decreases. We therefore successfully demonstrated the fabrication of a submicrometer RTD using a trilayer soft reflow technique that has the benefit of excellent scalability, high throughput, repeatable, and a reliable low-cost process.