For energy-constrained multi-sensing IoT devices, ultra-low-power queueing is one of the critical event-driven design challenges to capture low-speed sensing data with various sampling frequencies. In this paper, 0.3V 1W2R sub-threshold FIFO memory is proposed for ultra-low-voltage operations using Schmitt-Trigger (ST) 12.5T SRAM bit-cell, ripple bitline structure and cross-point data-aware write wordline scheme. The ST 12.5T memory bit-cell not only increases hold static noise margin (HSNM) but also eliminates write half-select disturbance for robust sub-threshold operation. Secondly, an adaptive timing tracing circuitry and negative bit-line circuits are employed in the design for PVT variation-tolerant read operation and write ability enhancement. Thirdly, the proposed ripple bitline structure divides the bitline into several segments for ultra-low-voltage operations. Thus, the access time can be reduced apparently. Finally, a 4kb sub-threshold FIFO memory with the proposed multi-port ST 12.5T bit-cells is implemented by UMC 28nm HKMG technology. The proposed FIFO memory can execute one write and two read operations simultaneously for multi-sensor IoT applications. The average power and maximum write frequency are 4.01 μ W and 780kHz at 0.3V, respectively.