Uncooled thermopile infrared detector linear arrays withdetectivity greater than 109 cmHz1/2/W

We have fabricated 63-element linear arrays of micromachined thermopile infrared detectors on silicon substrates. Each detector consists of a suspended silicon nitride membrane with 11 thermocouples of sputtered Bi-Te and Bi-Sb-Te films. At room temperature and under vacuum these detectors exhibit response times of 99 ms, zero frequency D* values of 1.4× 10⁹ cmHz^1/2/W and responsivity values of 1100 V/W when viewing a 1000 K blackbody source. The only measured source of noise above 20 mHz is Johnson noise from the detector resistance. These results represent the best performance reported to date for an array of thermopile detectors. A test procedure is described that measures many of the relevant electrical, optical, and thermal properties of the detectors without specialized test structures     

Thermal characterization of thermally-shunted heterojunctionbipolar transistors

Heterojunction Bipolar Transistors (HBTs) are potentially useful in a number of microwave applications, but they are severely limited by a current distribution instability caused by electrothermal interaction and the use of a low thermal conductivity substrate. A novel thermal management technique called “thermal shunting” has been developed to reduce thermal resistance and junction temperature non-uniformity. Thermal resistance measurements for thermally-shunted devices are presented. Specific thermal resistance measurements as low as 2.6×10^-4°C-cm²/W (147°C/W at 0.1 W for a device with a 177 μm² emitter area) have been obtained. Thermal resistance values obtained for thermally-shunted HBTs are substantially lower than those reported for conventional HBTs     

Free-standing AlGaAs thermopiles for improved infrared sensordesign

Our group introduced the GaAs/AlGaAs material system for various integrated and micromachined thermoelectric sensors. Investigating the material parameters of Al_xGa_1-xAs in detail indicates that this material system can be optimized with respect to thermoelectric properties. We demonstrate that figures of merit Z as high as 1.4×10^-4 K^-1 are predicted. Simultaneously, this material is compatible for micro-machining purposes. The presented infrared sensor is optimized with respect to the material parameter and design. The sensors do not need a supporting membrane and hence undesirable parallel thermal conductance is reduced. Sensors of different geometrical dimensions have been fabricated and compared. Black body measurements result in responsivities up to R=365 V/W and maximum relative detectivities of D^*=6.9×10⁸ cm√(Hz)/W which compare to the predicted performance     

AlGaN Photodetectors Prepared on Si Substrates

AlGaN ultraviolet (UV) metal-semiconductor-metal (MSM) photodetectors (PDs) grown on silicon substrates were fabricated and characterized. With 5-V applied bias, it was found that dark current density of Al_0.2Ga_0.7N PDs on silicon substrate was only 7.5times10^-9 A/cm². With an applied bias of 7 V, it was found that peak responsivities were 0.09 and 0.11 A/W while UV/visible rejection ratios (i.e., peak wavelength: 420 nm) were 324 and 278 for Al_0.2Ga_0.8N and Al_0.3 Ga_0.7N MSM PDs, respectively. Moreover, the noise equivalent power of Al_0.2Ga_0.8N MSM PDs was estimated to be 3.5times10^-12 W     

128元非致冷氧化钒红外探测器的制作

采用新工艺在氮化硅衬底上制备了室温时电阻温度系数为 - 0 .0 2 1K-1的氧化钒薄膜 ,以此为基础 ,利用光刻和反应离子刻蚀工艺在硅衬底上制作了 12 8元氧化钒红外探测器 .为了降低探测器敏感元与衬底间的热导 ,设计制作了自支撑的微桥结构阵列 .测试结果显示探测器的响应率和探测率在 8～ 12 μm的长波红外波段处分别达到10 4V/W和 2× 10 8cmHz1/ 2 W-1.     

Characterization of bolometers based on polycrystalline silicongermanium alloys

In this paper, we report on the first realization and characterization of uncooled Infra Red (IR) bolometers, based on polycrystalline alloys of silicon and germanium (poly SiGe). Responsivity, thermal conductance, thermal time constant and noise will be analyzed. It will be shown that poly SiGe provides high thermal insulation. An average detectivity of 10⁸ cm√(Hz)/W has been measured. We expect that modifications in the device structure could allow to achieve detectivities of 10⁹ cm √(Hz)/W     

Monolithic photovoltaic PbS-on-Si infrared-sensor array

The growth of epitaxial narrow-gap PbS-on-Si substrates using a stacked CaF₂-BaF₂ intermediate buffer layer and the fabrication of linear arrays of photovoltaic infrared (IR) sensors in the PbS layer are discussed. The sensors of the array exhibit resistance-area products at zero bias of 3 Ω-cm² at 200 K (3.4-μm cutoff wavelength) and 2×10⁵ Ω-cm ² at 84 K (4-μm cutoff), with corresponding detectivities of 2×10¹⁰ and 1×10¹³ cm-√Hz/W, respectively     

Experimental determination of electron drift velocity in 4H-SiC p+-n-n+ avalanche diodes

4H-SiC p⁺-n-n⁺ diodes of low series resistivity (<1×10^-4 Ω·cm²) were fabricated and packaged. The diodes exhibited homogeneous avalanche breakdown at voltages U_b=250-270 V according to the doping level of the n layer. The temperature coefficient of the breakdown voltage was measured to be 2.6×10^-4 k^-1 in the temperature range 300 to 573 K. These diodes were capable of dissipating a pulsed power density of 3.7 MW/cm² under avalanche current conditions. The transient thermal resistance of the diode was measured to be 0.6 K/W for a 100-ns pulse width, An experimental determination of the electron saturated drift velocity along the c-axis in 4H-SIC was performed for the first time, It was estimated to be 0.8×10⁷ cm/s at room temperature and 0.75×10⁷ cm/s at approximately 360 K     

Enhanced thermal contact conductance using carbon nanotube array interfaces

Heat-conduction interfaces that employ carbon nanotube (CNT) arrays have been fabricated and studied experimentally using a reference calorimeter testing rig in a vacuum environment with infrared temperature measurements. Arrays of multiwalled CNTs are grown directly on silicon substrates with microwave plasma-enhanced chemical vapor deposition. Iron and nickel were used as CNT catalysts. CNT arrays grown under different synthesis conditions exhibit different pressure-contact conductance characteristics. The thermal contact resistance of CNTs with a copper interface exhibits promising results with a minimum value of 19.8mm/sup 2/K/W at a pressure of 0.445MPa.     

Al/W/TiNx/TiSiy/Si barrier technology for1.0-μm contacts

A reliable contact diffusion barrier has been successfully formed by sintering in nitrogen a physically sputtered W/Ti bilayer. After a 650°C furnace anneal, a TiN_x/TiSi_y layer on contact with the silicon substrate was formed beneath the overlying W. No reaction between N₂ and W was observed. Arsenic implanted in the silicon substrate tended to retard the silicidation of titanium. Substantial redistribution of both B and As across the silicide layer was also observed during the contact sintering process. The 1.0-μ contacts fabricated with the Al/W/TiN_x/TiSi_y/Si barrier technology exhibited low and tightly distributed contact resistivities (less than 10^-6 Ω-cm²). No excessive leakage of the shallow junctions was observed even after thermally stressing the sample at 400°C for 8 h     

Growth and characterization of Indium-doped silicon for extrinsic IR detectors

Experimental growth and characterization studies of extrinsic indium-doped silicon for 3- to 5-µm focal-plane array applications have been carried out. Large, 2- and 3-in-diameter, -oriented indium-doped silicon crystals were prepared by Czochralski crystal pulling. The growth conditions affecting crystalline perfection, maximum dopant concentration and uniformity, and the residual shallow acceptor impurity content in grown crystals were investigated. In addition, effects of carbon content on the concentration of the 0.11-eV defect level in indium-doped silicon have been studied. The results demonstrate that near dislocation-free crystals containing indium concentrations up to 5 × 10¹⁷cm^-3can be achieved at low growth rates to delay the onset of constitutional supercooling, while unwanted boron and aluminum impurities can be maintained at levels approaching 1 × 10¹³cm^-3, when high purity synthetic-quartz crucibles are utilized to minimize melt contamination. Phosphorus-compensated indium-doped infrared (IR) detector performance and test photodetectors show peak responsivities up to 10 A/W (5.9 µm, 1000 V/cm, 50 K). Monolithic CCD test structures fabricated on Czochralski indium-doped silicon substrates show lower responsivities, however, due to detrimental effects of high-temperature CCD processing.     

The effect of compressive strain on the performance of p-typequantum-well infrared photodetectors

A detailed study of the performance of compressively strained p-type III-V quantum-well infrared photodetectors (p-QWIPs) is presented in this work. Three device structures composed of InGaAs-GaAs, InGaAs-AlGaAs, and InGaAs-AlGaAs-GaAs for normal incidence absorption have been fabricated and analyzed, with the results being compared with similar reported unstrained p-QWIPs. In all three QWIP structures, the quantum-well layers are under biaxial compressive strain ranging from -0.8% to -2.8%, while the barrier layers are lattice-matched to the substrate. The detection peaks of the quantum-well infrared photodetectors ranged from 7.4 to 10.4 μm. The detectors utilized the bound-to-continuum, bound-to-quasi-bound, and step bound-to-miniband intersubband transitions for infrared detection. The results showed that responsivities of up to 90 mA/W and detectivities from 10⁹ to over 10¹⁰ cm√Hz/W are achieved under moderate applied bias and at reasonable operating temperatures (from 60 to 80 K), demonstrating the viability of the strained-layer p-doped quantum-well infrared photodetectors for staring focal plane array applications     

Arrays of microdischarge devices having 50-100 μm squarepyramidal Si anodes and screen cathodes

Microdischarge devices having (50-100 μm)² pyramidal Si anodes and metal screen cathodes have been operated continuously at Ne gas pressures up to 1350 Torr and voltages below 95 V. More than 34 μW of output power is produced by a single device in a solid angle of ~5×10^-2 sr for a Ne pressure of 500 Torr. 3×3 arrays of these devices have been fabricated     

Carrier transport related analysis of high-power AlGaN/GaN HEMTstructures

Shubnikov-de Haas (SdH) oscillation and Hall measurement results were compared with HEMT DC and RF characteristics for two different MOCVD grown AlGaN-GaN HEMT structures on semiinsulating 4H-SiC substrates. A HEMT with a 40-nm, highly doped AlGaN cap layer exhibited an electron mobility of 1500 cm²/V/s and a sheet concentration of 9×10¹² cm at 300 K (7900 cm²/V/s and 8×10¹² cm^-2 at 80 K), but showed a high threshold voltage and high DC output conductance. A 27-nm AlGaN cap with a thinner, lightly doped donor layer yielded similar Hall values, but lower threshold voltage and output conductance and demonstrated a high CW power density of 6.9 W/mm at 10 GHz. The 2DEG of this improved structure had a sheet concentration of n_SdH=7.8×10¹² cm^-2 and a high quantum scattering lifetime of τ_q=1.5×10^-13 s at 4.2 K compared to n_SdH=8.24×10¹² cm^-2 and τ_q=1.72×10^-13 s for the thick AlGaN cap layer structure, Despite the excellent characteristics of the films, the SdH oscillations still indicate a slight parallel conduction and a weak localization of electrons. These results indicate that good channel quality and high sheet carrier density are not the only HEMT attributes required for good transistor performance     

Test structures to measure the heat capacity of CMOS layersandwiches

We report novel thermal characterization microstructures to measure the heat capacity of CMOS thin film sandwiches. This parameter is relevant, e.g., for the dynamic response of thermal CMOS microtransducers and for the thermal management of integrated circuits. The test structures were fabricated using a commercial 2-μm CMOS process, followed by maskless micromachining. The propagation of heat waves in the structures is monitored, which provides the thermal conductivity and heat capacity of CMOS thin film sandwiches. At 300 K, volumetric heat capacities of (1.71±0.12)×10⁶ Jm ^-3K^-1 and (2.41±1.88)×10⁶ Jm^-3K^-1 were obtained for the sandwich of CMOS dielectrics and for the lower CMOS metal, respectively. These values do not deviate significantly from available bulk data of such materials     

Thermal Boundary Resistance Between GaN and Substrate in AlGaN/GaN Electronic Devices

The influence of a thermal boundary resistance (TBR) on temperature distribution in ungated AlGaN/GaN field-effect devices was investigated using 3-D micro-Raman thermography. The temperature distribution in operating AlGaN/GaN devices on SiC, sapphire, and Si substrates was used to determine values for the TBR by comparing experimental results to finite-difference thermal simulations. While the measured TBR of about 3.3 x 10^-8 W^-1 ldr m² ldr K for devices on SiC and Si substrates has a sizeable effect on the self-heating in devices, the TBR of up to 1.2 x 10^-8 W^-1 ldr m² ldr K plays an insignificant role in devices on sapphire substrates due to the low thermal conductivity of the substrate. The determined effective TBR was found to increase with temperature at the GaN/SiC interface from 3.3 x 10^-8 W^-1 ldr m² ldr K at 150degC to 6.5 x 3.3 x 10^-8 W^-1 ldr m² ldr K at 275degC, respectively. The contribution of a low-thermal-conductivity GaN layer at the GaN/substrate interface toward the effective TBR in devices and its temperature dependence are also discussed.     

导热金刚石同大尺寸芯片的低温烧结银连接工艺

通过高导热银浆实现了连接大面积(＞100 mm2)半导体硅片和金刚石的低温低压烧结技术.通过对金刚石表面镀覆金属薄膜,增强同烧结银界面处固态原子扩散,开发了商用烧结银膏在200 ℃下低温烧结工艺,得到金刚石-硅的均匀连接界面,计算得到孔隙率约为9.88％,中间烧结银层等效热阻约为1.38×10-5m2·K/W.     

Electrical characterization of ultra-shallow junctions formed bydiffusion from a CoSi2 layer

Ultra-shallow p⁺/n and n⁺/p junctions were fabricated using a Silicide-As-Diffusion-Source (SADS) process and a low thermal budget (800-900°C). A thin layer (50 nm) of CoSi₂ was implanted with As or with BF₂ and subsequently annealed at different temperatures and times to form two ultra-shallow junctions with a distance between the silicide/silicon interface and the junction of 14 and 20 nm, respectively. These diodes were investigated by I-V and C-V measurements in the range of temperature between 80 and 500 K. The reverse leakage currents for the SADS diodes were as low as 9×10 ^-10 A/cm² for p⁺/n and 2.7×10^-9 A/cm² for n⁺/p, respectively. The temperature dependence of the reverse current in the p ⁺/n diode is characterized by a unique activation energy (1.1 eV) over all the investigated range, while in the n⁺/p diode an activation energy of about 0.42 eV is obtained at 330 K. The analysis of the forward characteristic of the diodes indicate that the p⁺ /n junctions have an ideal behavior, while the n⁺/p junctions have an ideality factor greater than one for all the temperature range of the measurements. TEM delineation results confirm that, in the case of As diffusion from CoSi₂, the junction depth is not uniform and in some regions a Schottky diode is observed in parallel to the n⁺/p junction. Finally, from the C-V measurements, an increase of the diodes area of about a factor two is measured, and it is associated with the silicide/silicon interface roughness     

Integral heat-sink IMPATT diodes fabricated using p+etch stop

The problems in batch fabrication of integral heat-sink IMPATT diodes are greatly simplified through a newly developed preferential etching technique. Devices fabricated utilizing the new technique have thermal resistance (θjc) values of 17-20°C/W for an active area of 2 × 10^-4cm².     

Low-resistance bandgap-engineeredW/Si1-xGex/Si contacts

Bandgap-engineered W/Si_1-xGe_x/Si junctions (p⁺ and n⁺) with ultra-low contact resistivity and low leakage have been fabricated and characterized. The junctions are formed via outdiffusion from a selectively deposited Si_0.7Ge _0.3 layer which is implanted and annealed using RTA. The Si _1-xGe_x layer can then be selectively thinned using NH₄OH/H₂O₂/H₂O at 75°C with little change in characteristics or left as-deposited. Leakage currents were better than 1.6×10^-9 A/cm² (areal), 7.45×10^-12 A/cm (peripheral) for p⁺/n and 3.5×10^-10 A/cm² (peripheral) for n⁺/p. W contacts were formed using selective LPCVD on Si_1-xGe_x. A specific contact resistivity of better than 3.2×10^-8 Ω cm² for p ⁺/n and 2.2×10^-8 Ω cm² for n⁺/p is demonstrated-an order of magnitude n⁺ better than current TiSi₂ technology. W/Si_1-xGe _x/Si junctions show great potential for ULSI applications