Although thermal IR microemitters making use of Honeywell planar technology
remain the devices of choice for the last decade, a significant disadvantage of these
devices is their two-level structure, which results in low fill-factor and causes
mechanical and thermal stresses between the layers. In this paper, the technology for
single-level polycrystalline SiGe thermal microemitters, their design, and performance
characteristics are presented. The 128-element linear arrays with a fill-factor of 88 %
and a 2.5-μm-thick resonant cavity have been grown by low-pressure chemical vapor
deposition and fabricated using surface micromachining technology. The 200-nm-thick
60 × 60 μm2 emitting pixels enforced with a U-shape profile pattern demonstrate
time response of 2-7 ms and an apparent temperature of 700 K in the 3-5 and 8-12 μm
atmospheric transparency windows. The SiGe device application to the infrared
dynamic scene simulation and critical factors that aid their competitiveness over
conventional planar two-level design are discussed.
The technology for the small-size focal plane arrays and linear arrays of polycrystalline SiGe microbolometers is developed at IMEC and successfully transferred to its industrial partner XenICs. A NETD of about 100 mK is achievable at the readout level on 14×14 and 200×1 arrays with 50 - 60 μm pixel pitch at a time constant of 20 - 25 ms. The design of pixels provides very precise tuning of the infrared resonant cavity. The resistance and TCR nonuniformity with σ/μ better than 0.2% combined with about 1% noise nonuniformity and 100% pixel operability are demonstrated. The first lot of arrays has been characterized, the arrays have been assembled with hybrid readout chips, supplied with the dedicated evaluation board and a software, and the results of system testing are being reported. The possibility to use the SiGe arrays as infrared emitters has been investigated for the first time and the results are presented as well.
The state-of-the-art characteristics of polycrystalline SiGe microbolometer arrays are reported. An NETD of 100 mK at a time constant of 25 ms is achievable on 14×14 and 200×1 arrays at the system level. It is the result of joint studies targeted at 1/f noise decrease, as well as TCR and uniformity improvements together with the design optimization. Thanks to successful decrease of 1/f noise of SiGe, the arrays were moved from "1/f-noise limited" to "system limited," i.e. to the case of VOx arrays. The mechanical design of pixels was improved affording very precise tuning of the infrared quarter-wave resonant cavity. The resistance and TCR non-uniformity with σ/μ better than 0.2% combined with about 1% noise nonuniformity and 100% pixel operability are demonstrated. The first lots of arrays with 99.98% production pixel yield have already been characterized and the results are being reported.
The state-of-the-art characteristics of micromachined polycrystalline SiGe microbolometer arrays are reported. An average NETD of 85 mK at a time constant of 14 ms is already achievable on typical self-supported 50 μm pixels in a linear 64-element array. In order to reach these values, the design optimization was performed based on the performance characteristics of linear 32-, 64- and 128-element arrays of 50-, 60- and 75-μm-pixel bolometers on several detector lots. The infrared and thermal modeling accounting for the read-out properties and self-heating effect in bolometers resulted in improved designs and competitive NETD values of 80 mK on 50 μm pixels in a 160x128 format at standard frame rates and f-number of 1. In parallel, the TCR-to-1/f noise ratio and the mechanical design of the pixels were improved making poly-SiGe a good candidate for a low-cost uncooled thermal array. The technological CMOS-based process possesses an attractive balance between characteristics and price, and allows the micromachining of thin structures, less than 0.2 μm. The resistance and TCR non-uniformity with σ/μ better than 0.2% combined with 99.93% yield are demonstrated. The first lots of fully processed linear arrays have already come from the IMEC process line and the results of characterization are presented. Next year, the first linear and small 2D arrays will be introduced on the market.
The performance characteristics of polycrystalline SiGe microbolometer arrays are the subject of both design and technological optimizations performed in this work to move the arrays towards the production. An NETD of 90 mK at a time constant of 11 ms is already achievable for the best non-optimized 60 micrometers pixel, 0.26 micrometers thick bolometer design in a linear 128 pixel array according to the results of LWIR characterization. The performance of linear 32, 64 and 128 element arrays of 50-, 60- and 75-micrometers pixel bolometers made with 0.26...0.13 micrometers thin poly-SiGe on several wafer runs was the starting point for the computer simulation of detector features and evolution of its characteristics under reading bias pulses. The material properties and parameters of read-outs are taken into account in the optimization of the design parameters of arrays as well. The typical bolometer characteristics achieved on the latest wafer run if processed with the PC-program accounting for the read-out and heating effects, result in an average NETD of 70 mK at a time constant of 17 ms for 50 micrometers pixels in a 320x240 array. Despite less TCR-to-1/f noise ratio as compared with VOx arrays, the several advantages make poly-SiGe a very attractive candidate for an uncooled array, i.e. full compatibility with CMOS technology, better characteristics/price ratio, resistance nonuniformity s/mean <0.2%, and a possibility to release extra-thin structures.
Extremely thin (50-100nm) polycrystalline silicon germanium (poly SiGe) microbolometers have been realized thanks to structural stiffness enhancement techniques within the pixel and the support legs. The technique involves the definition of U-shaped profiles using surface micromachining. This approach allows to decouple thermal isolation to some extent from thermal time constant. The result is a faster yet sensitive microbolometer compared to its thicker counterparts. Thermal time constants between 5 and 10 ms are achieved in vacuum yet the thermal conductance of the support legs is as low as the radiation limit (3x10-8 W/K). Apart from the (CMOS compatible) absorber definition and the release of the sacrificial oxide layer, the microbolometer process runs in a 8' Si CMOS pilot line and uses deep submicron stepper capability of the pilot line. The release process using vapor HF does not attack pixel, absorber or metal interconnect and leads to a yield close to or equal to 100%. Linear arrays and small 2D arrays of such microbolometers are demonstrated. To protect the bolometers in an early stage of the packaging, a zero-level (on-chip) flip-chip package based on indent-reflow sealing has been developed. The germanium window material is processed using process steps from multi-chip-module technology.
The results of experimental and theoretical investigations of the noise properties of high-Tc superconducting films and bolometers are reported. YBaCuO and GdBaCuO films produced by magnetron and laser deposition on various substrates were studied. The effect of various noise components on the noise equivalent power (NEP) of different bolometers is considered. Structural, noise and critical current properties were investigated. Using the laser ablation YBaCuO films with very low noise Hooge's parameter close to 2 X 10-4 was obtained. Experimental data are discussed on basis of the modern excess low frequency l/f models. Besides, the noise measurements of antenna YBaCuO microbolometers on NdGaO3 substrate and GdBaCuO bolometers on Si-membrane are reported. The NEP equals 1.2 X 10-11 W/Hz1/2 at response time of 0.3 microsecond(s) for microbolometer and D* equals 3.8 X 109 cmHz1/2W-1 at response time of 0.45 ms for bolometer on Si-membrane were reached. NEP of the bolometers is limited by only the phonon noise.