To adapt to the development trend of high-spatial-resolution of uncooled infrared detectors, the uncooled infrared focal plane array (IR FPA), which is the core component of uncooled infrared detectors, is constantly developing towards larger arrays and smaller pixels. Aiming at the diode-type IR FPA, this paper theoretically analyzes the influence of the sensitive element diode on the readout circuit and device performance. While determining the best operating current of the diode, the number of series connected in the diode structure and junction area are the leading performance factors. Based on this conclusion, a p+n-pn-n+p 3-in-1 diode was designed and combined with traditional diodes, “well”-shape diodes, p+n-n+p 2-in-1 diodes, and two 3-in-1 diodes obtained by the direct expansion of p+n-n+p 2-in-1 diodes, which were compared and investigated. The study found that the p+n-pn-n+p 3-in-1 diodes of the six structures had the most significant number of diodes in series under the same size, and the relative junction area was the largest. Using Sentaurus TCAD simulation, it was verified that under the same overall size, the voltage temperature sensitivity (TCV) value of the p+n-pn-n+p 3-in-1 diodes is approximately that of the p+n-n+p 2-in-1 diode, and two types diode of 3-in-1 obtained by direct expansion on the p+n-n+p 2-in-1 diode was 1.5 times, which is 2.6 times and 3.7 times the “well” shape diode and traditional diode, respectively. It is proved that the performance of the p+n-pn-n+p 3-in-1 diode is the best under small pixels, and the expansion of the N-in-1 diode can further optimize the device performance.