Performance Characterization of Infrared Detectors Based on Polymorphous Silicon‐Germanium (pm‐Si_xGe_1−x:H) Thin Films Deposited at Low Temperature

Abstract

In this work, the fabrication of infrared detectors (uncooled microbolometers) using surface micromachining techniques is presented. The thermo-sensing film used in the devices is polymorphous silicon-germanium (pm-Si x Ge 1Àx :H) produced by low frequency plasma-enhanced chemical vapor deposition (PECVD) at low temperature (200 C). Polymorphous semiconductors basically are amorphous semiconductors with embedded nanocrystals (of diameter of about 2-5 nm), which are formed during the film deposition. The presence of nanocrystals impacts on the properties of the material by reducing the density of states (defects) and improving the stability of the films. For infrared detectors those materials present important properties such as high temperature coefficient of resistance (TCR ¼ À4.7% K À1 ), long-term stability, low deposition temperature, and silicon CMOS compatibility. Test structures with size of 50 Â 50 μm 2 and different thermal isolation designs are characterized under IR radiation (0.7-20 μm) in a frequency range of 5-100 Hz. From voltage responsivity and noise measurements, the specific detectivity is calculated achieving values of 1 Â 10 8 cm Hz 1/2 W À1 and thermal response time of 8-9 ms under 150 nA bias current. The above characteristics make those devices very suitable for the development of infrared focal plane arrays (IRFPAs).

Abnormal hump in low temperature in SiGe devices with silicon capping insertion layer

“…The electronic defects at the interface will then act as carrier scattering centers and consequently cause the current-voltage (I-V) characteristics and the channel mobility to degrade. The C-V characteristics will also be affected by these defects through frequency dispersion and stretch out [12][13][14][15][16][17]. Hence, an understanding of the interfacial quality of SiGe MOS capacitance (MOSCAP) structures is important.…”

Fabrication of Microbolometer Arrays Based on Polymorphous Silicon–Germanium

“…In previous work, titanium (Ti) electrodes were on the top of the membrane [28,29], however, there were problems of stress mismatching between Ti and pm-Si x Ge 1-x :H. Now we have decided to replace the coplanar electrodes with Ti studs; in addition, an array of microbolometers with pixel area of 50 × 50 µm 2 was fabricated in order to study the stability of the structures and analyze their performance quality.…”

Reactive Force-Field Molecular Dynamics Study of SiGe Thin Film Growth in Plasma Enhanced Chemical Vapor Deposition Processes

“…In this paper, as an example, we focused on silicon-germanium (SiGe) thin films deposited by PECVD using Silane (SiH4) and Germane (GeH4), and hydrogen molecules (H2). SiGe thin films, such as hydrogenated amorphous SiGe (a-SiGe:H) and hydrogenated microcrystalline SiGe (μc-SiGe:H), are potential candidates for thin film solar cells (14), infrared detectors (15), micro-electro-mechanical systems (MEMS) (16), and biomedical devices (17). However, the relationship between properties, structure/composition, and materials/processes are still unclear.…”