High-resistivity Silicon Wafer Research Articles

Analysis of lattice deformation originated from residual stress on performance of aluminum nitride-based bulk acoustic wave resonators

With the development of MEMS technology to the nanometer scale, the influence of different process conditions on the performance of nano-devices can be calculated through the microscopic changes of materials. During the manufacturing process, the large residual stress from the film stack significantly influences the performance of devices, thereby reducing the wafer yield. Herein, we apply density functional theory to MEMS processes to reveal the intrinsic mechanism of how residual stress affects the performance of aluminum nitride-based bulk acoustic wave (BAW) resonators on an 8-inch high-resistance silicon wafer. The variation rule of physical properties of piezoelectric material aluminum nitride with different residual stresses is calculated via first-principles calculations. Through theory formula derivation, the piezoelectric-coupling constant (Kt2) of the bulk acoustic wave resonator is positively correlated with tensile residual stress, and the resonant frequency (fp, fs) is negatively correlated with tensile residual stress. The measurement results show that the average shifts of Keff2 is 0.12 % within −137 MPa and 183 Mpa residual stress, which is an excellent match with the theory prediction.

Structure and RF performance evolution of polycrystalline silicon charge capture layer for advanced RF-SOI in in-situ annealing process

In this paper, the structures and radio-frequency (RF) properties of high resistivity silicon (HR-Si) wafers with a polycrystalline silicon (Poly-Si) charge capture layer after in-situ annealing were investigated. The thermal treatment significantly improves the wafer warpage and optimize the resistivity of Poly-Si/HR-Si interfaces. By using spreading resistance profiling (SRP), energy dispersive spectrometer (EDS) and secondary ion mass spectrometry (SIMS) technology, the rise of interfacial resistivity may be as results of the pyrolysis of the native oxide and the diffusion of hydrogen atoms. The transmission Kikuchi diffraction (TKD) analysis exhibited that the grains were recrystallized during the annealing, leading to the transformation from the small angle boundaries (SAGBs) into low-Σ coincidence lattice grain boundaries (CSL GBs). The drop of the bulk resistivity of the Poly-Si layer is attributed to the reduction of the total grain boundary (GB) density and the increase of the low electro-activity GB density. Moreover, the microwave losses and non-linearity of the RF-SOI with embedded Poly-Si layer was evaluated by on-chip testing based on CPW. It was determined that the decrease in the Poly-Si resistivity only worsens the microwave losses but not the non-linearity.

Development of photo-diodes for Pohang-Accelerator-Laboratory X-ray free-electron laser

The Pohang-Accelerator-Laboratory X-ray free-electron laser (PAL-XFEL) provides intense ultra-short X-ray pulses via a self-amplified spontaneous emission (SASE) process. Since fluctuations are induced by the intrinsic characteristics of the SASE process, we designed and fabricated photo-diodes (PDs) to be used in quadrant beam position and pop-in monitoring systems for measuring intensity and position, and beam size, respectively. Six 500μm-thick high-resistivity silicon wafers were used for different fabrication processes to vary the thicknesses of bias electrode and anti-reflective coating layers optimized for the quantum efficiency (QE) at typical wavelengths of 266 and 400 nm used for pump–probe experiments at the PAL-XFEL. In this paper, we present the electrical characteristics, QE, signal-to-noise ratio, energy resolution of the fabricated PDs, and compared them with those of commercial PD.

On the depletion behaviour of low-temperature covalently bonded silicon sensor diodes

Low temperature covalent direct wafer-wafer bonding allows for the fusion of multiple semiconductor wafers without any additional material at the bonding interface. In the context of particle pixel detectors this might provide an alternative to bump-bonding for joining sensors to readout chips. Previous investigations have shown that the amorphous layer formed at the interface during bonding is detrimental to charge propagation. To investigate the influence of the bonding interface on signal collection we have fabricated custom test structures by bonding high-resistivity N to high-resistivity P-type silicon wafers thus forming P-N junctions. Scanning transmission electron microscopy shows indeed the formation of ca. 3 nm wide amorphous layer at the interface. Using a scanning transient current technique (TCT) setup we were able to record generated signals. Illuminating our sample with light of different wavelengths and from different sides, indicates that the P side of the bonded structures can be fully depleted, but not the N side. This indicates a strongly asymmetric depletion behaviour which we attribute to the presence of the bonding interface.

Investigation on time-dependent behavior of resistivity in high-resistivity silicon wafers

As a cornerstone of 5G, high-resistivity silicon on insulator plays an important role in telecommunications. But it is still a great challenge to measure the resistivity of high-resistivity silicon wafer quickly and accurately. Comparing to other methods, four-point probe (4PP) techniques are considered as the preferable approach. The time-dependent behavior of high-resistivity silicon wafer were first observed during 4PP measurement and the variation of chemical elements on the wafer surface was studied by X-ray photoelectron spectrum. The resistivity of P-type silicon decreases with storage time, while that of N-type silicon increases, which can be attributed to the surface energy band bending due to the variation of the interface states during native oxidation on wafer surface. The first-principles calculation was carried out to observe the effect of interface states on the electrical properties. Based on mechanism of time-dependent behavior of high-resistivity silicon, a thermal treatment method was proposed to realize stable resistivity rapidly for high-resistivity silicon wafer.

Analysis of dielectric constant behavior of thermally treated SU-8 polymer up to 18 GHz

Su-8 polymer has excellent potential for application in process manufacturing. This paper presents the effects of thermal stress on the electromagnetic properties of SU-8 polymer, showing the frequency-dependent microwave response of the material. The procedure follows the international standard method for assessing the quality of components and devices for space qualification as thermal stress simulates the aging process. The polymer has been used as a base layer to fabricate passive devices in the coplanar waveguide (CPW) configuration. Resonating structures and delay lines, with different sizes, have been manufactured on a SU-8 layer spun on a high resistivity silicon wafer. The material's dielectric constant has been calculated by measuring the microwave response of the devices before and after the thermal processes. We have recorded data in a broadband range, from 2 GHz to 18 GHz, and the conclusive comparison allows us to identify a frequency dependence of the electromagnetic performances of SU-8 polymer and confirms the possibility to use it for medium- and long-term microwave space applications. Specifically, minor changes of the electrical matching have been recorded in the Ku-band, from 12 GHz to 18 GHz, making the polymer reliable for current space communications.

Using silicon disk resonators to measure mechanical losses caused by an electric field.

Several projects of the next generation gravitational-wave detectors use the high purity monocrystalline silicon test masses. The electric field of the actuator that is applied to correct the position of the silicon test mass causes additional mechanical losses and associated noise. Disk mechanical resonators are widely used to study mechanical losses in multilayer optical coatings that are deposited on the test masses of gravitational-wave detectors. We use silicon disk resonators to study losses caused by an electric field. In particular, the dependence of mechanical losses on the resistivity of silicon is investigated. The resonator is a thin commercial silicon wafer in which a low frequency nodal diameter mode is excited. A DC voltage is applied between the wafer and a nearby electrode. We use two measurement configurations. In the first configuration, the dependence of losses on the resistance in the voltage supply circuit is investigated. The dependence of losses on the resistivity of silicon is investigated in the second configuration. We propose a model that relates the electric field induced mechanical loss in disk resonators to the resistivity of the material. Measurements are carried out for low and high resistivity silicon wafers. The measurement results are compared with calculations. Based on these studies, it is possible to estimate the loss and noise of the test masses of gravitational-wave detectors associated with electrostatic actuators.

All-silicon, low-cross-talk terahertz waveguide crossing based on effective medium.

All-silicon effective-medium-clad waveguides are a promising candidate for an integrated terahertz platform with high efficiency and broad bandwidth. Waveguide crossings are essential circuit components, allowing for wave routing over shorter paths to increase circuit density. However, the simple intersection of two orthogonal effective-medium-clad waveguides results in terahertz wave scattering, leading to relatively high cross talk. In this work, a low-loss, 40% fractional bandwidth crossing utilizing Maxwell-Garnet effective-medium theory and wavefront planarization techniques is proposed. This monolithic structure is fabricated on a single high-resistivity float-zone silicon wafer using a deep reactive ion etching process with a modest 4.4 mm diameter (4.03λ0) structure footprint. Experimentally verified results show low insertion loss, less than 1 dB, and average cross talk level of -39dB for both E11x and E11y operating modes, over 220-330 GHz with a 40% fractional bandwidth. This waveguide crossing can be foreseen as a useful routing component for terahertz all-silicon integrated circuits. The proposed techniques are applicable to other dielectric waveguide platforms at infrared and optical frequencies.

Effective-medium-clad Bragg grating filters

We propose a series of integrated Bragg grating filters with performance enhancement via the concept of effective medium. The bandstop filters are built in a high-resistivity silicon wafer and operated over the WR-3.4 band (220–330 GHz) with in-plane polarization. The proposed designs use an additional degree of freedom in controlling the effective refractive index so as to fully use the potential of the Bragg grating structures. As a result, the high insertion loss typically observed at the low-frequency bound of the filters due to weak wave confinement can be reduced, while radiation caused by the leaky-wave effect at the high-frequency bound is minimized, allowing for a 40% operation fractional bandwidth. These features are not achievable with conventional waveguide Bragg grating filters. All-silicon prototypes of filter samples are experimentally validated, demonstrating promising performance for a wide range of terahertz applications. The techniques to improve the filter characteristics by controlling the effective medium can be adopted in both microwave and optics domains.

Study of Nanowire-Based Integrated via Technology for CMOS Application in Millimeter-Wave Frequencies

This work shows a novel integrated via structure based on 1.2- μm thick copper nanowires (NWs) for use in CMOS applications at millimeter-wave frequencies. Coplanar waveguide (CPW) lines are fabricated on a 5000-Ω-cm high-resistivity silicon wafer and connected by NW vias that are grown in integrated anodized alumina oxide (AAO). The AAO layer is fabricated by anodizing an evaporated aluminum layer onto the silicon wafer. This cointegrated technology has 0.095-dB insertion loss for 0.3-mm long circuits with two vias at 40 GHz. The results are promising with an estimated loss per via of approximately 0.0275 dB. The fabricated structure shows great performance agreement with its reference test circuits of similar length. The design comparisons of circuits with different via dimensions and positions show that the shorter the via length, the wider the via width; and placing the via on the CPW ground plane closer to the signal line provides better performance.

Multifunctionalities of 2D MoS2 self-switching diode as memristor and photodetector

Self-switching diodes (SSD) were fabricated at the wafer level on a 2D few-layer MoS 2 thin film (7 monolayers) grown on a 4-inch Al 2 O 3 /high-resistivity silicon wafer via Chemical Vapor Deposition (CVD). We report here that MoS 2 behaves as a transparent piezoelectric material in the near infrared spectral region and as a strain-induced ferroelectric material with a measured d 33 piezoelectric coefficient of 3–10 pm/V depending on the applied AC voltage. Moreover, we demonstrate experimentally that the SSDs behave as lateral memristors and as photodetectors in the visible spectrum, with responsivities as high as 17 A/W.

Characteristics of Effective-Medium-Clad Dielectric Waveguides

Effective-medium-clad dielectric waveguides are purely built into a single high-resistivity float-zone silicon wafer with their claddings defined by deep subwavelength perforations. The waveguides are substrate-free while supporting both $E_{11}^x$ and $E_{11}^y$ modes with low loss and low dispersion. This article extends the investigations of the waveguides by analyzing the dispersion, cross-polarization, and crosstalk together with the characteristics of bends and crossings over an operation frequency range of 220–330 GHz (WR-3 band). Taking the $E_{11}^x$ mode as an example, the experimental results show an average measured attenuation coefficient of 0.075 dB/cm and a group velocity dispersion ranging from around $\pm$ 10 ps/THz/mm across the whole band. A crosstalk level below $-$ 10 dB is measured for parallel waveguides with a separation of 0.52 $\lambda _{0}$ at 300 GHz. The realized waveguides show a bending loss ranging from 0.500 to 0.025 dB per bend and a crosstalk at crossing below $-$ 15 dB from 220 to 330 GHz. Due to the different dispersion characteristics, the $E_{11}^y$ mode has similar performances but with its operation frequency range reduced to 260–330 GHz. Limited by the measurement setup, a cross-coupling between the $E_{11}^x$ and $E_{11}^y$ modes is measured to be below $-$ 20 dB over the whole band. This in-depth investigation of effective-medium-clad waveguides will form a basis for terahertz-integrated platforms.

Terahertz Dispersion and Amplification under Electron Streaming in Graphene at 300 K

We interpret the recent observations of Otsuji’s team (Sendai) on switching from absorption to amplification at a temperature of T = 300 K during the passage of terahertz radiation through hexagonal boron nitride–graphene sandwiches with multiple gates on the surface with an increase in the electric field in graphene. It is shown that these effects are related to dispersion and negative conductivity near the transit-time frequency of electrons in momentum space under streaming (anisotropic distribution) in graphene in a strong electric field. On the basis of these data, a universal tunable terahertz source is proposed, which has the form of a graphene-containing sandwich with a high-resistance silicon wafer (a cavity) with an applied voltage. This terahertz cavity is a complete analog of the microwave generator implemented on an InP chip by Vorobev’s team (St. Petersburg).

Characterization of the low temperature behavior of thin Titanium/Titanium Nitride multilayer films

Titanium and titanium nitride layers were alternately sputtered on a high resistivity silicon wafer to obtain a multilayer film structure, for a total thickness ranging between 34 and 180 nm. The electrical resistance of the Ti/TiN film was characterized from room temperature down to the superconducting transition. Both the resistivity just above the transition and the critical temperature were investigated as a function of the total film thickness and the single TiN layer thickness, respectively. The obtained resistivity range is 67–312 μΩ cm. Exploiting the proximity effect, we were able to tune the critical temperature in the 0.29–4.5 K range. A comparison between experimental data and theoretical models is proposed in order to facilitate the a priori design of superconducting detectors.

Терагерцовые дисперсия и усиление при стриминге электронов в графене при 300 K

Abstract We interpret the recent observations of Otsuji’s team (Sendai) on switching from absorption to amplification at a temperature of T = 300 K during the passage of terahertz radiation through hexagonal boron nitride–graphene sandwiches with multiple gates on the surface with an increase in the electric field in graphene. It is shown that these effects are related to dispersion and negative conductivity near the transit-time frequency of electrons in momentum space under streaming (anisotropic distribution) in graphene in a strong electric field. On the basis of these data, a universal tunable terahertz source is proposed, which has the form of a graphene-containing sandwich with a high-resistance silicon wafer (a cavity) with an applied voltage. This terahertz cavity is a complete analog of the microwave generator implemented on an InP chip by Vorobev’s team (St. Petersburg).

Behavior of gold-doped silicon substrate under small- and large-RF signal

In this paper, small- and large-signal performances of passive devices integrated on high-resistivity, trap-rich and gold-doped silicon wafers are presented and compared through measurements and simulations. The gold-doped silicon substrate was produced starting from standard silicon having a nominal resistivity of 56 Ω·cm. We show that the gold-doped substrate presents high effective resistivity and low losses suitable for RF applications. This has been demonstrated by measuring coplanar waveguides, crosstalk, inductors and band pass filter where we observed similar performances for small-signal measurements compared with trap-rich substrate. Large-signal measurements of gold-doped substrates show 60 dBm lower harmonic distortion than high-resistivity substrates, and 10 dB lower than trap-rich substrate at 0 V DC bias. However, a large DC bias dependence on the harmonic distortion induced by the gold-doped substrate is observed. This unexpected behavior is explained using the Fermi level localization in the silicon bandgap for the different DC bias conditions.

Attenuation of THz Beams: A \u201cHow to\u201d Tutorial

Attenuation of ultrashort THz pulses poses a significant technological challenge due to the broadband nature of such light pulses. Several methods exist for this purpose, including crossed wire grid polarizers, high refractive index, high resistivity silicon wafers, and ultrathin metal films. In this review, we discuss the operational principles of these methods, and highlight some of the advantages and potential pitfalls of the methods. We describe the limits of high-frequency operation of wire grid polarizers, relevant for contemporary ultra-broadband THz sources in air photonics. We discuss the effects of multiple reflections and interference in sequences of silicon wafers for attenuation, and finally discuss the potential of using ultrathin metallic films for broadband attenuation.

Thin-Film SUEX as an Antireflection Coating for mmW and THz Applications

We present a simple process for depositing SUEX dry films to realize effective antireflection coatings on high-resistivity silicon wafers and lenses. Heat-assisted conformal deposition of SUEX film followed by curing via ultraviolet exposure achieves robust adhesion to the silicon lens surface. Due to its relatively low material loss and commensurate refractive index, quarter-wavelength-thick SUEX coatings minimize reflection losses and significantly improve signal coupling into high-index silicon lenses. As an example, a 150- $\mu$ m-thick SUEX layer was conformally coated on a 1-cm-diameter high-resistivity silicon lens to reduce reflection loss to less than 4% over the 220–325 GHz band.

On-chip single-mode high-Q terahertz whispering gallery mode resonator

The chip-scale terahertz (THz) devices and systems are helpful to enable actual applications in THz communication and sensing. Here, we demonstrate an on-chip THz whispering gallery mode resonator (WGMR) delivering a high-quality (Q) factor TE single mode, fabricated on a high-resistivity float zone silicon wafer by complementary metal–oxide–semiconductor compatible technology. For a TE mode in a WGMR, it is the first time to achieve a Q factor of 1210 at 0.4925 THz with 28 dB extinction ratio, to the best of our knowledge. With this excellent WGMR, we have demonstrated a stable and highly sensitive sensor for particle distance estimation. Our investigation provides an effective approach to fabricate high-performance integrated THz-WGMRs for chip-scale systems.

THz Laser Beam Profiling by Homogeneous Photodoping of High Resistivity Silicon in a Compact Single-Pixel Detection Setup

A compact single-pixel detection scheme for terahertz (THz) beam profiling is demonstrated. It incorporates an optical amplitude modulator that uses photodoping of a high resistivity Silicon (HR-Si) wafer with near-infrared (NIR) binary intensity masks, to modulate transmission of THz radiation through the semiconductor. A 270 nm thick indium-tin-oxide thin film deposited on glass by radio-frequency magnetron sputtering is used as dichroic mirror, such that the NIR radiation is brought at the Si wafer and the THz radiation is directed toward the detector, in a compact and efficient design. Given that homogeneous and well-defined binary masks in the form of structured intensity profiles of the NIR laser beam were needed, a beam homogenizer based on the Kohler integrator is also implemented. The profile of a THz laser beam with the wavelength of 118.8 μm was recorded using a resolution of 32 × 32 pixels and a square imaging area of 169 and 400 mm2, respectively. Also, due to the tunable nature of the laser system and symmetry of the laser cavity, more than one transverse modes of the laser cavity were imaged, namely, TEM00 and TEM01. A beam diameter of 3.25 mm in the TEM00 mode was recorded and a modulation depth of 52% at 2.5 THz was achieved with the present setup. With this paper, a THz spatial-domain imaging setup based on single-pixel method and having a compact design is proposed. Its functionality and possibility of further development are shown.