Microbolometers Based on Amorphous Silicon–Germanium Films With Embedded Nanocrystals

Abstract

In this paper, we have fabricated and characterized uncooled microbolometers using as infrared element intrinsic amorphous silicon-germanium films with embedded nanocrystals with a dimension in the range of ∼2-4 nm. The presence of nanocrystals in the amorphous films reduces the density of defects, improves the transport properties, and specially improves the films stability against radiation. On the other hand, the combination of silicon and germanium in one alloy allows to improve the film conductivity and the temperature coefficient of resistance (TCR), without the necessity of perform doping. Large values of TCR have been demonstrated in the microbolometers, as large as −6.6% K −1 , which in fact is the largest value reported for this kind of devices, and consequently large detectivity values were obtained in the reported devices (2 × 10 9 cmHz 1/2 W −1 ).

Mean Free Path of Photoelectronic Excitations in Hydrogenated Amorphous Silicon and Silicon Germanium Alloy Semiconductors

“…[ 12,13,15,17–20 ] Incorporation of either carbon or germanium into a‐Si:H also alters the film resistivity, temperature coefficient of resistance, and 1/ f noise, which impact microbolometer performance. [ 30–32,34–37 ]…”

“…Hydrogenated amorphous silicon (a-Si:H) and related thin films have been implemented in device applications, including absorbers in thin film solar cells, [11][12][13][14][15][16][17][18][19][20][21] passivation layers in wafer silicon photovoltaics, [22][23][24][25][26][27][28] and imaging layers in uncooled infrared (IR) sensing microbolometers. [29][30][31][32][33][34][35][36][37] The a-Si:H network varies in terms of incorporated hydrogen content and bonding configuration, [23,26,[38][39][40][41] the presence of nanoscale voids and vacancy structures, [38,39] and film stress [42] as deduced from experimental measurements. The formation of short and long filamentary structures, bond length distributions, and bond angle distributions has been identified through advanced computational modeling.…”

“…[12,13,15,[17][18][19][20] Incorporation of either carbon or germanium into a-Si:H also alters the film resistivity, temperature coefficient of resistance, and 1/f noise, which impact microbolometer performance. [30][31][32][34][35][36][37] For plasma-enhanced chemical vapor deposited (PECVD) a-Si:H-based materials developed for such device applications, spectra in the complex optical response in the form of the complex dielectric function (ε ¼ ε 1 þ iε 2 ) obtained by in situ real time spectroscopic ellipsometry (RTSE) have been reported to vary as functions of deposition and processing conditions, [11,14,16,17,21,[23][24][25][26][32][33][34]41,[45][46][47][48][49][50][51] alloying with carbon or germanium, [45][46][47][48][49][50] post-deposition plasma or annealing treatments, [28,49] accumulated film thickness, [21,51] and underlying substrate material.…”

Advanced numerical investigation of the heat flux in an array of microbolometers

“…Due to the high level of rarefaction, the simulation of gas flow in a micro-cavity that encloses an array of microbolometers 1–5 is much more challenging than in the classical flow regimes: the low number of gas molecules encapsulated in the considered domain make their mean free path much longer than usual, so the diffusive description used in the continuum approach (Navier-Stokes equations) ceases to be valid. The degree of rarefaction of a gas in such micro-systems is generally defined by the Knudsen parameterwhere λ is the mean free path of the molecule and L the characteristic dimension of the system.…”

Performance Characterization of Infrared Detectors Based on Polymorphous Silicon‐Germanium (pm‐SixGe1−x:H) Thin Films Deposited at Low Temperature

“…That features enables shrinking pixel size which results in several technological advances as: larger format arrays (1024 × 768), smaller and cheaper optical systems and packages . Recently an alloy of silicon (Si) and germanium (Ge) consisting of a mixed phase of an amorphous matrix with embedded nanocrystals (referred as polymorphous silicon, pm‐Si x Ge 1−x :H) has shown promising results due to its high TCR, its high stability against radiation, and the possibility to tailor its properties by controlling the Ge content in the films, without the necessity of perform doping . In this work, we present microbolometers fabricated with a intrinsic pm‐Si x Ge 1−x :H thermo‐sensing film.…”