MTF performance: measurements, modelisation, and optimization for Sofradir II-VI IR photodetectors

Abstract

SOFRADIR is widely present on the IR detector market for high-performance space, military and security applications thanks to a well mastered Mercury Cadmium Telluride (MCT) technology, and to the recent acquisition of the III-V InSb, InGaAs, and QWIP technologies. As a result, strong and continuous development efforts are deployed to deliver cutting edge products with improved performances in terms of sensitivity, spatial and thermal resolution. The actual trend in quantum IR detector development is the design of very small pixel, with high operating temperature. The selfconfinement of neighboring diodes may not be efficient enough to maintain optimal modulation transfert function (MTF). This paper presents the recent developments achieved in Sofradir in terms of MTF measurements protocol challenged by the pitch reduction. An overview of state of the art MTF results with optimized measurement technic will be shown, from SWIR to VLWIR MCT focal plane. In order to optimize device performances and reduce development cycle time, this experimental approach has been coupled with finite elements modelisation (FEM). Optimized MTF results for 10µm pitch and HOT MCT technology will be exposed.

10μm pitch design ofHgCdTediode array in Sofradir

“…The FPA has been optimized to reduce crosstalk and increase MTF values at Nyquist frequency [9]. Figure 6 presents the MTF of devices A and B as a function of spatial frequency.…”

“…The MTF represents the ability of the system to distinguish contrast for different spatial frequencies. Therefore it can be used to quantify the resolution capability [9]. Usually, the pixel in a FPA is not an ideal and isolated device.…”

“…The optimum of MTF can be reached without degrading the others FOM. Simulations show that 0.51 can be obtained at Nyquist frequency [9]. …”

Update on 10μm pixel pitch MCT-based focal plane array with enhanced functionalities

“…The MTF represents the ability of the system to distinguish contrast for different spatial frequencies. Therefore it can be used to quantify the resolution capability [6]. Usually, the pixel in a FPA is not an ideal and isolated device.…”

“…Furthermore, following this technological optimization trend, first experimental results on Device C shows an additional gain of at least 6 points is expected. The value of 0.51 can be obtained at Nyquist frequency [6]. The device A was already at comparable performance level as the 10µm InSb technology [9].…”