Fabrication of Microbolometer Arrays Based on Polymorphous Silicon-Germanium.

Ricardo Jimenez,Jorge Castro-Ramos,Eduardo Cano,Daniel Ferrusca,Arturo Ponce,Jose Rangel-Magdaleno,Julio Hernandez-Perez,Alfredo Morales,Mario Moreno,Alfonso Torres

doi:10.3390/s20092716

Abstract

This work reports the development of arrays of infrared sensors (microbolometers) using a hydrogenated polymorphous silicon–germanium alloy (pm-SixGe1-x:H). Basically, polymorphous semiconductors consist of an amorphous semiconductor matrix with embedded nanocrystals of about 2–3 nm. The pm-SixGe1-x:H alloy studied has a high temperature coefficient of resistance (TCR) of 4.08%/K and conductivity of 1.5 × 10−5 S∙cm−1. Deposition of thermosensing film was made by plasma-enhanced chemical vapor deposition (PECVD) at 200 °C, while the area of the devices is 50 × 50 μm2 with a fill factor of 81%. Finally, an array of 19 × 20 microbolometers was packaged for electrical characterization. Voltage responsivity values were obtained in the range of 4 × 104 V/W and detectivity around 2 × 107 cm∙Hz1/2/W with a polarization current of 70 μA at a chopper frequency of 30 Hz. A minimum value of 2 × 10−10 W/Hz1/2 noise equivalent power was obtained at room temperature. In addition, it was found that all the tested devices responded to incident infrared radiation, proving that the structure and mechanical stability are excellent.

Highlights

Semiconductor materials with characteristics of low resistivity and high temperature coefficient of resistance (TCR) are important for detection of infrared radiation by uncooled microbolometers, which are widely used in the range of 8–12 μm, known as LWIR
We study the implementation in microbolometer arrays of a hydrogenated polymorphous silicon-germanium alloy, which is a material composed of an amorphous matrix with embedded nanocrystals in the range of 2–3 nm [23]
A scanning electron microscope (SEM) picture of a section of the microbolometer array is shown in Figure 5a, while Figure 5b shows an image of one 50 × 50 μm22 microbolometer

Summary

Introduction

Semiconductor materials with characteristics of low resistivity and high temperature coefficient of resistance (TCR) are important for detection of infrared radiation by uncooled microbolometers, which are widely used in the range of 8–12 μm, known as LWIR (long-wave infrared). A microbolometer is a thermal detector where a resistive membrane absorbs infrared radiation, which increases its temperature. The increase in temperature reduces the resistance of the membrane and the measurement of the change of resistance is the output of the sensor. A high TCR is desirable to increase the sensitivity of the device or maintaining it when it is desired to reduce the pixel area. A low resistivity makes it easier to read the pixels with the associated ROIC (readout integrated circuit). The resistivity of the material directly influences the 1/f noise and the performance of the devices

Methods

Results

Conclusion