Resistivity Si Research Articles

Effect of silicidation on silicon-based thin film resistors in SiGe integrated circuits

The resistance variation of the silicon–germanium (SiGe) thin film resistor caused by the fabrication process of SiGe integrated circuits (ICs) was investigated. The SiGe resistor and the Si resistor were made of the thin films identical with the p-type SiGe base layer and the n-type Si emitter layer of the SiGe hetero-junction bipolar transistor, respectively. The range of the resistance value of the SiGe resistor was much larger than that of the Si resistor, and an abnormally high resistance of the SiGe resistor was often observed. Ti–B precipitates and Ti(Si1−xGex)2 protrusions were created as the result of the Ti silicidation of the p-type SiGe layer, whereas no precipitates and protrusions were generated in the case of the n-type Si layer. It was confirmed by scanning electron microscopy that the nonuniform resistance of the SiGe resistor was induced by the removal of the protrusions and underlying field oxides in the contact window. Resistance uniformity of the SiGe resistor was much improved by increasing the contact size. The simulation result of the detrimental influence of the resistance change on ICs indicated that the fabrication process and the structure of the thin film resistor should be optimized for enhancing IC reliability.

FERROELECTRIC VARACTOR SHUNT SWITCHES FOR BROADBAND PHASE CONTROL APPLICATIONS

ABSTRACT Our research group has recently demonstrated the operation of ferroelectric varactor shunt switches. The device operation is based on the nonlinear dielectric tunability of a barium strontium titanate (BST 60/40) thin-film sandwiched between two metal layers in a parallel plate configuration. A 4:1 change in the varactor capacitance has been achieved with a bias voltage < 10 V, through optimization of the nanostructured BST thin-film fabrication process on high resistivity Si substrates. In this work, we investigated the varactor shunt switches for broadband phase control applications. Varactor shunt switches and cascaded shunt switches were used for phase control circuits, due to the large phase shifts possible as a result of the dc bias dependent tunability of the varactor. The differential phase shift can be defined as the difference between the phase of S21 at a dc bias voltage and zero-bias. The measured differential phase shift for a single varactor shunt switch was 30 ± 2 degrees between 8 and 26 GHz at 8 V dc bias. A cascaded varactor shunt switch resulted in a differential phase shift of 110 degrees ± 10 degrees over the bandwidth of 20 and 31 GHz.

2.4 GHz ISM-Band Receiver Design in a 0.18 $\mu{\hbox{m}}$ Mixed Signal CMOS Process

This letter presents the design and measurement results of a fully integrated CMOS receiver front-end and voltage controlled oscillator (VCO) for 2.4 GHz industrial, scientific and medical (ISM)-band application. For low cost design, this receiver has been fabricated with a 0.18 mum thin metal CMOS process with a top metal thickness of only 0.84 mum. The receiver integrates radio frequency (RF) front-end (a single-ended low-noise amplifier (LNA) with on-chip spiral inductors and a double balanced down conversion mixer), VCO and local oscillation buffers on a single chip together with an internal output buffer. To obtain the high-quality factor inductor in LNA, VCO and down conversion mixer design, patterned-ground shields (PGS) are placed under the inductor to reduce the effect from image current of resistive Si substrate. Moreover, in VCO and mixer design, due to the incapability of using thick top metal layer of which the thickness is over 2 mum, as used in many RF CMOS process, the structure of dual-metal layer in which we make electrically short circuit between the top metal and the next metal below it by a great number of via arrays along the metal traces is adopted to compensate the Q -factor degradation. In this letter, the receiver achieves a conversion gain of 23 dB, noise figure of 8.1 dB and P1 dB of -20 dBm at 39 MHz with 21 mW power dissipation from a 1.8 V power supply. It occupies a whole circuit area of 2 mm2.

The fabrication and material properties of compositionally multilayered Ba1−xSrxTiO3 thin films for realization of temperature insensitive tunable phase shifter devices

Compositionally layered BaxSr1−xTiO3 (Ba0.60Sr0.40TiO3–Ba0.75Sr0.25TiO3–Ba0.90Sr0.10TiO3) 220nm thin film heterostructures were fabricated on Pt coated high resistivity Si substrates via the metal organic solution deposition technique (MOSD). Optimization of the material design was achieved by evaluating two integration schemes, namely, the single- and multianneal process protocols. Materials characterization demonstrated that both film process protocols resulted in smooth, dense, crack-free films with a single phase perovskite structure. Rutherford backscattering spectroscopy revealed compositionally distinct layers and severe elemental interdiffusion for the films fabricated via the multianneal and single-anneal process protocols, respectively. The retention of the compositional layering subsequent to film crystallization deemed the multianneal processed BaxSr1−xTiO3 (BST) film suitable for evaluation of dielectric properties. The dielectric properties were compared to both paraelectric uniform composition BST and to the relevant compositionally graded BST films reported in the technical literature. Our results made evident that the multiannealed compositionally layered BST films possessed higher permittivity (εr=360) and lower dissipation factor (tanδ=0.012) with respect to both uniform composition paraelectric Ba0.60Sr0.40TiO3 film fabricated via the same MOSD processing method and the relevant literature values for compositionally graded BST films. The multilayered BST material design exhibited minimal dielectric dispersion in the range of 90to−10°C, showing a 6.4% decrease in permittivity (corresponding to a temperature coefficient of capacitance TCC20–90=−0.921) as the temperature was elevated from 20to90°C and only a 2.1 increase in permittivity (TCC20–(−10)=−0.716) as the temperature was lowered from 20to−10°C. Additionally, the dielectric tunability of the multilayered BST structures over the temperature range of −10–90°C was temperature independent. Our results show that the multilayered BST design has excellent dielectric properties and the enhanced tunability and dielectric loss are stable over a relatively broad temperature range (−10–90°C), thereby making them excellent candidates for the next generation of enhanced performance temperature stable tunable devices.

Tunable (Ba, Sr)TiO3 interdigital capacitor onto Si wafer for reconfigurable radio

AbstractIn this article, the potential feasibility of integrating BST films into Si wafer by adopting tunable interdigital capacitor (IDC) with TiO2 thin film buffer layer is suggested. TiO2 as buffer layer is grown onto Si substrate by atomic layer deposition and the coplanar IDC on BaxSr1−xTiO3(500 nm)/TiO2(50 nm)/high resistivity Si (HR‐Si) is fabricated. BST interdigital tunable capacitors integrated on HR‐Si substrate with high tunability and low loss tangent are characterized for their microwave performances. BST/HR‐Si and BST/TiO2/HR‐Si IDCs show much enhanced tunability values of 31% and 40%, respectively as compared to the value of 21% obtained with BST film on MgO single crystal substrate at the bias of 5 kV/cm. BST/TiO2/HR‐Si structure shows much improved figure of merit of 504.4 as compared to 418.53 and 101.68 of BST/MgO and BST/HR‐Si structure, respectively. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2144–2148, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22657

Realization of AlGaN/GaN HEMTs on Si‐on‐polySiC substrates

AbstractAlGaN/GaN High Electron Mobility Transistors have been realized on resistive Si(111)/SiO2/polySiC substrates. The epitaxial structures were grown by Molecular Beam Epitaxy. The structural, optical, and electrical properties of these films are studied and compared with those of reference heterostructures grown on thick Si(111) substrates. Channel mobility of 1470 cm2/Vs at room temperature and sheet carrier density of 6.65x1012 cm–2 have been achieved. Field effect transistors with 3.6 µm x 100 µm gates have been fabricated on these layers and exhibit a drain current superior to 450 mA/mm and a transconductance of 123 mS/mm. Furthermore, to evaluate the influence of heat transfer onto electrical properties, the resistance change with the power dissipated inside Transmission Line Measurement devices has been compared with those in devices realized with layers grown on thick Si(111) and 4H‐SiC substrates. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Development of NiO-based thin film structures as efficient H 2 gas sensors operating at room temperatures

P-type NiO thin films have been developed on high resistivity Si and SiO 2 substrates by a pulsed laser deposition technique using an ArF ⁎ 193 nm excimer laser at deposition temperature of 300 °C and in 40 Pa partial oxygen pressure. Structures based on such NiO films as host material in the form of Au–NiO Schottky diodes have been subsequently developed under vacuum. In a different procedure, an n-SnO 2 layer has been deposited by a CVD technique on a NiO film to produce a p/n heterojunction. The sensing properties of all above structures have been tested upon exposure to a H 2 flow in air ambient gas at various operating temperature ranging from 30 to 180 °C. For the NiO films, the optimum temperature was about 150 °C exhibiting a sensitivity of 94%. After surface sensitization of NiO by Au the NiO films showed an H 2 response at operating temperature of 30 °C. The sensitivity of p-NiO/n-SnO 2 heterojunction devices was extracted from I– V measurements in air and under H 2 flow mixed in air. In this case a dramatic increase of the sensitivity was achieved at operating temperature of 30 °C for a forward bias of 0,2 V.

Terahertz pulse reflective focal-plane tomography

An effective terahertz (THz) imaging technology is presented for achieving tomographic image. A THz pulse reflective focal-plane imaging system is built up and the tomographic image of a metallic cross hidden by a high resistivity Si wafer is achieved. Using the reflected pulses from each interface, the thickness of each layer can be calculated with calculation error below 2.5%. This work demonstrates that the THz pulse focal-plane tomography can be used to analysis interior configuration of the object.

Microwave performance of thin film ferroelectric varactors in the wide temperature range of −223 °C to +227 °C

Parallel-plate Au(Pt)/Ba 0.25Sr 0.75TiO 3/(Pt)Au thin film varactors are fabricated on high resistive Si substrate and characterized at 1 MHz and microwave frequencies up to 45 GHz in the temperature range of −223 °C to +227 °C. The relative tunability of capacitance decreases with temperature, as capacitance does, from 80 to 90% at −193 °C down to 10% at +227 °C. The temperature coefficient of capacitance in the temperature range −55 to +125 °C is approximately 0.3% at 20 GHz and zero dc field. The temperature dependence of the varactor loss tangent, in general, follows that of the capacitance. The loss tangent at zero dc field and 20 GHz is less than 0.1 at −193 °C and less than 0.02 at +227 °C. The figure of merit of the varactor, taking into account both the tunability and the loss tangent, at 20 GHz is more than 1000 at −193°C and 50 at +227 °C.

Low frequency and microwave performances of Ba0.6Sr0.4TiO3 films on atomic layer deposited TiO2/high resistivity Si substrates

We report on high tunablity of Ba0.6Sr0.4TiO3 (BST) thin films realized through the use of atomic layer deposited TiO2 films as a microwave buffer layer between BST and a high resistivity (HR) Si substrate. Coplanar waveguide (CPW) meander-line phase shifters using BST/TiO2/HR-Si and BST/MgO structures exhibited a differential phase shift of 95∘ and 24.4∘, respectively, at 15 GHz under an electric field of 10 kV/cm. The figure of merit of the phase shifters at 15 GHz was 30.6∘/dB for BST film grown on a TiO2/HR-Si substrate and 12.2∘/dB for BST film grown on a MgO single crystal substrate. These results constitute significant progress in integrating BST films with conventional silicon technology.

Re‐configurable Kμ dual‐bands slot antenna using mems switches

AbstractReconfigurability in an antenna system is a desired characteristic that has been the focus of much research in recent years. The paper demonstrates miniature re‐configurable antenna designed and fabricated on the high resistivity Si substrate. This antenna can integrate with a novel microelectromechanical systems actuator for reconfiguring the operating frequency and is used for SoC (System on the chip). The switching between the two different frequency bands is achieved through the use of RF‐MEMS switches. According to the open/closed experiment results, when switch is on and off, the antenna operating frequency is 12.3 GHz and 13.1 GHz with low return loss, respectively. The final model radiates at two widely separated frequencies with very similar radiation patterns. The proposed concept can be extended to reconfigurable linear antenna arrays or to more complex antenna structures with large improvements in antenna performance. It is important for the next generation wireless communications and integrated antenna system on the chip. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2413–2416, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21979

Temperature dependent microwave performance of AlGaN/GaN high-electron-mobility transistors on high-resistivity silicon substrate

The influence of temperature (− 50 °C to + 200 °C) was studied on the DC and microwave characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs) on high resistivity Si substrate for the first time. The AlGaN/GaN HEMTs exhibited a current-gain cut-off frequency ( f T) of 11.8 GHz and maximum frequency of oscillation ( f max) of 27.5 GHz. When compared to room temperature values, about 4% and 10% increase in f T and f max and 23% and 39.5% decrease in f T and f max were observed when measured at − 50 °C and 200 °C, respectively. The improvement of I D, g m f T, and f max at − 50 °C is due to the enhancement of 2DEG mobility and effective electron velocity. The anomalous drain current reduction in the I– V curves were observed at low voltage region at the temperature ≤ 10 °C but disappeared when the temperature reached ≥ 25 °C. A positive threshold voltage ( V th) shift was observed from − 50 °C to 200 °C. The positive shift of V th is due to the occurrence of trapping effects in the devices. The drain leakage current decreases with activation energies of 0.028 eV and 0.068 eV. This decrease of leakage current with the increase of temperature is due to the shallow acceptor initiated impact ionization.

High temperature pulsed measurements of AlGaN/GaN HEMTs on high resistive Si(111) substrate

AbstractDC‐ and RF‐pulsed measurements of AlGaN/GaN HEMTs on high resistive silicon (111) substrate are achieved under probes in the 300–525 K temperature range. Current collapse and heating effects are studied and it demonstrates the high temperature properties of these devices. Hence the potential of this technology for power applications at microwave frequencies is confirmed. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2301–2305, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21897

Characterization of an Integrable Single-Crystalline 3-D Tactile Sensor

Porous-Si-micromachining technique was used for the formation of single-crystalline force-sensor elements, capable of resolving the three vector components of the loading force. Similar structures presented so far are created from deposited polycrystalline Si resistors embedded in multilayered <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$hboxSiO_2/hboxSi_3hboxN_4$</tex> membranes, using surface micromachining technique for a cavity formation. In this paper, the authors implanted four piezoresistors in an n-type-perforated membrane, having their reference pairs on the substrate in order to form four half bridges for the transduction of the mechanical stress. They successfully combined the HF-based porous-Si process with conventional doping and Al metallization, thereby offering the possibility of integration with readout and amplifying electronics. The <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$300 times 300 muhboxm^2$</tex> membrane size allows for the formation of large tactile arrays using single-crystalline-sensing elements of superior mechanical properties. They used the finite-element method for modeling the stress distribution in the sensor, and verified the results with real measurements. Finally, they covered the sensors with different elastic silicon–rubber layers, and measured the sensor's altered properties. They used continuum mechanics to describe the behavior of the rubber layer.

Epitaxial Growth of SiGe Interband Tunneling Diodes on Si(001) and on Si0.7Ge0.3 Virtual Substrates

We present room temperature current voltage characteristics from SiGe interband tunneling diodes epitaxially grown on highly resistive Si(001) substrates. In this case, a maximum peak to valley current ratio (PVCR) of 5.65 was obtained. The possible integration of a SiGe tunnel diode with a strained Si transistor lead us to investigate the growth of SiGe interband tunneling diodes on Si 0.7 Ge 0.3 virtual substrates. A careful optimization of the layer structure leads to a maximum PVCR of 1.36 at room temperature. The latter value can be further increased to 2.26 at 3.7 K. Our results demonstrate that high quality SiGe interband tunneling diodes can be realized, which is of great interest for future memory and high speed applications.

Signal Transmission Characteristics between Si Chips with Air Gap using Si Integrated Dipole Antennas

Transmission characteristics of integrated linear dipole antennas fabricated on Si substrates were investigated for inter-chip signal transmission of wireless interconnections of Si ultra-large scale integrated circuits. Linear dipole antennas 1–6 mm long were fabricated on oxidized P-type Si substrates with resistivities of 10, 79.6, and 2290 Ω·cm. The transmission characteristics were investigated in the frequency and time domains. The transmission gain of a 4-mm-long dipole antenna fabricated on a 2.29 kΩ·cm resistivity Si substrate was -10 dB for a distance of 3 mm. A Gaussian monocycle pulse with a pulse width of 70 ps and a bandwidth of 20 GHz was transmitted and received successfully between Si chips with an air gap.

Composite right/left handed transmission line phase shifter using ferroelectric varactors

A composite right/left handed (CRLH) transmission line (TL) phase shifter, using ferroelectric (Ba/sub 0.25/Sr/sub 0.75/TiO/sub 3/) varactors as tunable element, is presented for the first time. It is theoretically and experimentally demonstrated how the unique features of CRLH TLs, enables a differential phase shift with flat frequency dependence around the center frequency. The experimental prototype is a coplanar design integrated on a high resistive Si substrate. It includes four CRLH T-unit cells and has a physical length of 3850/spl mu/m. The ferroelectric varactors are realized in parallel plate version. Under 15-V dc bias applied over each varactor, the differential phase shift is flat around 17GHz and has an absolute value of 50/spl deg/.

Integration of coplanar (Ba,Sr)TiO/sub 3/ microwave phase shifters onto Si wafers TiO/sub 2/ buffer layers

In this paper, a Ba0.6Sr0.4TiO3 (BST) tunable phase shifter with TiO2 films as microwave buffer layer between BST and silicon (Si) substrates is presented. The TiO2 buffer layer is grown by atomic layer deposition (ALD) onto Si substrate followed by pulsed laser deposition (PLD) of BST thin films onto the TiO2 buffer layer. The phase shifter fabricated on BST films grown on TiO2/Si substrate shows a good figure of merit (FOM) of 75.4 degrees/dB by exhibiting improved tunablity while retaining an appropriate dielectric Q as compared to 55.1 degrees/dB of BST/MgO structure. The TiO2 buffer layer grown by ALD enables successful integration of BST-based microwave tunable devices with high resistive Si wafer.

AlGaN∕GaN HEMTs on (001) silicon substrates

AlGaN/GaN high electron mobility transistors have been realised on resistive Si(001) substrate. The heterostructure was grown by molecular beam epitaxy. The 2D electron gas formed at the AlGaN/GaN interface exhibits a sheet carrier density of 7.1×1012 cm−2 and a Hall mobility of 1500 cm2/V s at room temperature. High electron mobility transistors with a gate length of 3 µm have been processed and DC characteristics have been achieved. A maximum drain current of more than 440 mA/mm and a transconductance gm of 120 mS/mm have been obtained. These encouraging results open the way for GaN-based electronic applications on Si(001) substrates.

High-tunability and low-microwave-loss Ba0.6Sr0.4TiO3 thin films grown on high-resistivity Si substrates using TiO2 buffer layers

In this Letter, we report on high-tunability and low-microwave-loss properties of Ba0.6Sr0.4TiO3 (BST) thin films by use of atomic-layer-deposited TiO2 films as the microwave buffer layer between BST and high-resistivity Si substrate. The interdigital capacitor fabricated on BST films grown on TiO2∕high resistivity Si (2kΩcm) substrates showed the much enhanced tunability value of 33.2% while retaining an appropriate Q factor, as compared to the tunability values of BST (21%) films grown on MgO single-crystal substrates and BST (8.2%) films grown on TiO2∕normal Si (10Ωcm) substrates. The coplanar waveguide BST phase shifter fabricated on TiO2∕high resistivity Si exhibited a phase shift of 95° and insertion loss of 3.09 dB at 15 GHz and an applied voltage of 50 V. ALD-grown TiO2 buffer layers enable the successful integration of BST-based microwave tunable devices onto high-resistivity Si wafers.