Nb_5 N_6 microbolometer arrays for terahertz detection

A novel room-temperature microbolometer array chip consisting of an Nb5N6 thin film microbridge and a dipole planar antenna, which is used as a terahertz （THz） detector, is described in this paper. Due to the high-temperature coefficient of the resistance of the Nb5N6 thin film, which is as high as –0.7% K-1 , such an antenna-coupled microbolometer is ideal for detecting signals in a frequency range from 0.22THz to 0.33THz. The dc responsivity, calculated from the measured I–V curve of the Nb5N6 microbolometer, is about –760 V/W at a bias current of 0.19mA. A typical noise voltage as low as 10 nV/Hz 1/2 yields a low noise equivalent power （NEP） of 1.3×10-11W/Hz 1/2 at a modulation frequency above 4kHz, and the best RF responsivity, characterized using an infrared device measuring method, is about 580V/W, with the corresponding NEP being 1.7×10-11W/Hz 1/2 . In order to further test the performance of the Nb5N6 microbolometer, we construct a quasi-optical type receiver by attaching it to a hyperhemispherical silicon lens, and the result is that the best responsivity of the receiver is up to 320V/W. This work could offer another way to develop a large scale focal-plane array in silicon using simple techniques and at low cost.

高灵敏太赫兹阵列检测器的低噪声读出电路

本文基于Nb5N6微测辐射热计(microbolometer)低噪声、高阻抗和高响应率的特性,为1 ×64阵列的Nb5N6 microbolometer设计了极低噪声的多通道读出电路。读出电路包含直流偏置电路,一、二级放大电路和多通道选择电路等几个部分,对检测器阻抗变化具有较强的鲁棒性,成功实现对64通道的微弱电压信号的放大和采集。电路具有优异的低噪性能,测量且分析比较了电路噪声对Nb5N6 microbolometer的影响。电路单通道输入阻抗达100 kΩ,增益约为60 dB,带宽约为30 kHz,噪声约为8.6 nV/Hz1/2。

Research on the response model of microbolometer

There are certain limitations in the application of uncooled focal plane array （FPA） detector due to the lack of an effective response model which reliably transforms the target temperature to analog output voltage. This paper establishes the response model of microbolometer through researching the detection theory of microbolometer and the heat balance equation under the condition of the pulsed voltage bias. In the establishing process, we simplified the heat balance equation to acquire a simple answer. The experimental data show that, in the temperature dynamic range of 30 K, the biggest tolerance between the model data and the experiment data is 0.2 K; while in the temperature dynamic range of 100 K, it is 1 K. This model can reflect the real response of the microbolometer with only small differences which are acceptable in engineering applications.

Readout circuit with nonuniformity correction for the uncooled microbolometer

The output of uncooled microbolometer is nonuniform, and the traditional two-point nonuniformity correction method requires a tight restriction on substrate temperature. The circuit proposed by this article can relax the restriction on the substrate temperature and perform nonuniformity correction when reading out the image signal. The dummy pixels reduce static current. And the Column shared DACs transfer correction data to the gates of MOS transistors and the positive reference edge of amplifier, to control the bias current of detector and dummy one, and set the start point of integration. This circuit has higher sensitivity, wider dynamic range, and frame frequency of more than 30 Hz for 128×128 array. PSPICE simulation results seem that this circuit functions well.

Improved Non-uniformity Correction Method for Uncooled Microbolometer

The uncooled microbolometer has a severe temperature requirement for non-uniformity correction. An improved two-point non-uniformity correction method is proposed, which can operate in wider uniform substrate temperatures. This method can control the bias voltage of MOS transistors by memory and DAC to meet two restrictions about responsivity and offset before traditional two-point calibration is implemented. The simulation results seem that this non-uniformity correction can work at uniform substrate temperature with fluctuant range of 4K.

Challenges in using an analog uncooled microbolometer thermal camera to measure crop temperature

It has been long known that thermal imaging may be used to detect stress(e.g.water and nutrient deficiency)in growing crops.Developments in microbolometer thermal cameras,such as the introduction of imaging arrays that may operate without costly active temperature stabilization,have vitalized the interest in thermal imaging for crop measurements.This study focused on the challenges occurring when temperature stabilization was omitted,including the effects of focal-plane-array(FPA)temperature,camera settings and the environment in which the measurements were performed.Further,the models for providing thermal response from an analog LWIR video signal(typical output from low-cost microbolometer thermal cameras)were designed and tested.Finally,the challenges which typically occur under practical use of thermal imaging of crops were illustrated and discussed,by means of three cereal showcases,including proximal and remotely based(UAV)data acquisition.The results showed that changing FPA temperature greatly affected the measurements,and that wind and irradiance also appeared to affect the temperature dynamics considerably.Further,it is found that adequate settings of camera gain and offset were crucial for obtaining a reliable result.The model which was considered best in terms of transforming video signals into thermal response data included information on camera FPA temperature,and was based on a priori calibrations using a black-body radiation source under controlled conditions.Very good calibration(r^(2)>0.99,RMSE=0.32℃,n=96)was obtained for a target temperature range of 15-35℃,covering typical daytime crop temperatures in the growing season.However,the three showcases illustrated,that under practical conditions,more factors than FPA temperature may need to be corrected for.In conclusion,this study shows that thermal data acquisition by means of an analog,uncooled thermal camera may represent a possible,cost-efficient method for the detection of crop stress,but appropriate corrections of disturbing factors are required in order to obtain sufficient accuracy.

Research on VOx uncooled infrared bolometer based on porous silicon

In this paper, vanadium oxide thin film of TCR of -3.5%/K has been deposited by pulsed DC magnetron sputtering method. The property of this VOx has been investigated by X-ray diffractometer （XRD） and atomic force microscopy （AFM） in detail. XRD test indicates that this film is composed of V203, V305 and VO2.VOx microbolometer with infrared （IR） absorbing structure is fabricated based on porous silicon sacrificial layer technology. Optimized micro-bridge structure is designed and carried out to decrease thermal conductance and this structure shows good compatibility with micromachining technology. This kind of bolometer with 74% IR absorption of 8-14μm, has maximum detectivity of 1.09×109cm.Hz]/2/W at 24Hz frequency and 9.81aA bias current.

A low-cost infrared absorbing structure for an uncooled infrared detector in a standard CMOS process

This paper introduces a low-cost infrared absorbing structure for an uncooled infrared detector in a standard 0.5 m CMOS technology and post-CMOS process. The infrared absorbing structure can be created by etching the surface sacrificial layer after the CMOS fabrication, without any additional lithography and deposition procedures. An uncooled infrared microbolometer is fabricated with the proposed infrared absorbing structure.The microbolometer has a size of 6565 m2and a fill factor of 37.8%. The thermal conductance of the microbolometer is calculated as 1.3310 5W/K from the measured response to different heating currents. The fabricated microbolometer is irradiated by an infrared laser, which is modulated by a mechanical chopper in a frequency range of 10–800 Hz. Measurements show that the thermal time constant is 0.995 ms and the thermal mass is 1.3210 8J/K. The responsivity of the microbolometer is about 3.03104V/W at 10 Hz and the calculated detectivity is 1.4108cm Hz1=2/W.