Ultrathin Silicon Research Articles

Atomistic modelling of electron propagation and radiation emission in oriented bent ultra-thin Si and Ge crystals

Computational modeling of passage of high-energy electrons through crystalline media is carried out by means of the relativistic molecular dynamics. The results obtained are compared with the experimental data for 855 MeV electron beam incident on oriented bent ultra-thin (15 microns) silicon and germanium crystals. The simulations have been performed for the geometries of the beam–crystal orientation that correspond (i) to the channeling regime and (ii) to the volume reflection. A comparison with the experiment is carried out in terms of angular distributions of the electrons deflected by the crystals bent with different curvature radii as well as of the spectra of the emitted radiation. For both crystals a good agreement between the simulated and experimentally measured data is reported. The origin of remaining minor discrepancies between theory and experiment is discussed.

Study on the recrystallization microstructure and texture evolution of a rolled 0.075 mm ultra-thin grain-oriented silicon steel

This paper investigated the recrystallization behavior of a rolled 0.075 mm ultra-thin grain-oriented silicon steel, and microstructure and texture evolutions were studied. At the early stage, dominant {hk0}<001> recrystallized grains were ascribed to the preferential {hk0}<001> nucleation, then their growth was reduced by texture pinning effect. In contrast, a few ‘random’ grains grew excessively to consume surrounding {hk0}<001> fine-grained matrix, meanwhile nuclei originating from initial non-Goss grains also showed size advantage and further grew. Despite of quasi-two-dimensional microstructure of ultra-thin sheet, the anisotropic surface energy did not show marked effect on grain growth difference. Those coarse grains, which were 10 times larger than the matrix grains, were surrounded by high energy (HE) boundaries, indicating that their growth was driven by high grain boundary mobility. With the increasing annealing time, the formation of {hk0}<001> oriented assemblies and the growth of non-{hk0}<001> oriented grains contributed to the overall grain size increase. Regarding the relationship between microstructure, texture and magnetic properties, {hk0}<001> texture was weakened and reduced magnetic induction accordingly, and the combination of growing while heterogeneous grain size and changing texture made iron loss a first decrease and then increase tendency. It is essential to control annealing time to obtain suitable combination of microstructure and texture.

Research on silicon wafer surface phase under the Ultra-thin slicing process and its etching hindrance behavior during metal-assisted chemical etching

Ultra-thin silicon slicing technology plays a critical role in achieving high-efficiency and low-cost solar cells in the photovoltaic (PV) industry. However, the surface phase evolution of silicon wafers under an ultra-thin slicing process and resulting etching behavior remains unclear. In this study, the surface phase evolution of different surface thicknesses of silicon wafers was carefully studied. As the thickness of silicon wafers became relatively thin, the degree of surface stress-induced amorphous silicon (ST-α-Si) significantly increased. Moreover, the UPS test showed that the ST-α-Si layer had an orbital energy level relatively lower than that in monocrystalline silicon, thereby having lower reduction performance during metal-assisted chemical etching (MACE). A copper deposition experiment was conducted to study the etching hindering effect caused by silicon surface ST-α-Si phases. The result showed that the presence of ST-α-Si adversely affected copper deposition. To improve the MACE uniformity, a pretreatment involving the use of HF/H2O2 mixed solution to remove the surface ST-α-Si layer was investigated. After HF/H2O2 pretreatment, the uniformity of inverted pyramids formed through MACE on the silicon wafer surface was significantly improved. Moreover, the reflectance of the MACE-textured surface was reduced to 7.67 % from 10.1 % compared with that without pretreatment. Therefore, this study provides reference guidelines and useful approaches for preparing uniform inverted pyramid surfaces using MACE in ultra-thin silicon wafers.

Evolutions of Cube ({001}) and {115} Orientations in Cold-Rolled Ultra-Thin Non-Oriented Silicon Steel.

In this study, the evolutions of Cube and {115}<161> orientations of a cold-rolled ultra-thin non-oriented silicon steel were investigated using a combination of experimental investigation and the crystal plasticity finite element method (CPFEM). The results show that Cube orientations remain relatively stable when their initial deviation angles from the ideal Cube orientation are less than 12°, even after a 60% cold rolling reduction. However, larger deviations occur due to higher strain near grain boundaries. Furthermore, the {115}<161> orientations, with an initial deviation of ~18° from the ideal Cube orientation, become separated into different orientation regions during cold rolling. Some regions gradually approach the ideal Cube orientation as cold rolling progresses and reach ~12.5° deviation from the ideal Cube at a 40% reduction. This study demonstrates good agreement between simulation and experimental results, highlights the micro-deformation mechanisms during rolling, and offers insights for optimizing the ultra-thin strip rolling process.

Investigation of perfect narrow-band absorber in silicon nano hole array

In this paper, we proposed a triple layer structure consisting of the bottom silver layer, thin silicon oxide space layer, and ultrathin semiconductor silicon film with nano hole array achieving three absorption peaks with narrow band. The absorption spectrum can be easily controlled by adjusting the structural parameters including the radius and period of the nano hole array, and the maximal absorption can reach 99.0% and the narrowest full width of half maximum can reach about 6.5 nm in theory. We also clarified the physical mechanism of the proposed structure in details by finite-difference time-domain simulation, in which the three narrow band perfect adsorption peaks can be attributed to electric dipole resonance, magnetic dipole resonance and plasmonic resonance respectively. At the same time, we used a low-cost nanosphere lithography method to fabricate the proposed nano hole array in large area. In experiment, the absorption peak of the proposed triple layer structure can reach up to 98.3% and the narrowest full width of half maximum can reach up to about 10.1 nm. The highest quality factor Q can reach up to 98.4. This work can open a new avenue for high-quality factor narrow band perfect absorption using ultrathin semiconductor film and benefit for many fields such as infrared sensors, plasmonic filters, and hyperspectral imaging.

High-speed and high-precision control of laser stealth dicing equipment based on interpolation and fitting

As an advanced wafer dicing technology, stealth dicing has the advantage of better-cutting quality and faster-cutting speed than traditional blade dicing technology and has a broad application prospect for the future cutting of large and ultra-thin silicon wafers. The stealth dicing equipment involves two processes, i.e., wafer altimetry and follow-through processing in silicon wafer cutting, the altimetry accuracy of which determines the processing precision. In this paper, polynomial fitting, linear interpolation, and cubic spline interpolation are applied to predict the altimetry data at different speeds to achieve high-speed and high-precision altimetry under various speed conditions. The research shows that the prediction accuracy of the three methods is less than 1 μm. The linear interpolation has the highest accuracy during the altimetry speeds of 500 mm/s ~ 1500 mm/s. The polynomial fitting can achieve better prediction results by selecting the best fitting parameter when the altimetry speeds are 1500 mm/s ~ 2500 mm/s. The cubic spline interpolation is more suitable for the processing of data sampled at altimetry speeds between 2500 mm/s and 3000 mm/s.

Ultrathin four-quadrant silicon photodiodes for beam position and monitor applications: Characterization and radiation effects

Ultrathin semiconductor photodiodes are of interest for beam position and monitoring in X-ray synchrotron beamlines and particle therapy medical applications. In this work, single and four-quadrant diodes have been fabricated on ultrathin Si films with thicknesses of 10 μm, 5 μm and 3 μm from silicon on insulator (SOI) substrates. Physical and electrical characterization of the devices has been carried out. Good functional electrical characteristics have been obtained for the devices fabricated on the different silicon thicknesses. The impact of electron, neutron and proton irradiations on the electrical characteristics has been studied for the 10 μm-thick devices. In spite of the observed diode leakage current increase and positive charge trapping in interquadrant isolation oxide, functional operation as radiation detector is verified upon illumination with a pulsed laser beam transient current technique.

Ultrathin, Flexible, and Reusable Silicon Shadow Masks Manipulated via Transfer Printing

Stencil lithography is a facile patterning technique that offers a potential solution to the limitations of conventional photolithography. However, several critical factors such as enhanced pattern resolution, ability to pattern on nonplanar surfaces, and multilayer patterning should further be addressed to extend the applications of stencil lithography. This study presents a novel ultrathin silicon shadow mask which is flexible, reusable, and able to be precisely aligned and manipulated through transfer printing. The small thickness of the silicon shadow mask inherently provides it with the enhanced resolution patterning on both planar and nonplanar surfaces. To highlight these attractive benefits, substrates are patterned with metal deposition as well as by etching in a multilayer configuration. Moreover, it is found that the pattern resolution which is degraded as the shadow mask is repeatedly coated with metal and becomes warped can be restored after the mask cleaning procedure, demonstrating its effective reusability. Finally, as a device‐level application, top contact/bottom gate organic thin film transistor arrays are fabricated on both planar and curved surfaces using the shadow mask. These results show the promise of stencil lithography as a versatile and reliable high resolution patterning method for various applications by exploiting the presented ultrathin silicon shadow mask.

Effect of the diamond saw wires capillary adhesion on the thickness variation of ultra-thin photovoltaic silicon wafers during slicing

In order to improve the performance of solar cells and reduce their manufacturing costs, monocrystalline silicon wafers used for manufacturing solar cells are developing towards larger sizes and ultra-thin thickness, and the diameter of diamond saw wires used to cut silicon wafers is also continuously decreasing. These aspects cause uneven thickness and lager thickness variation (TV) of the as-cut wafer during slicing process. The reason of uneven thickness was analyzed from the point of liquid bridge with capillary force between the saw wires in this paper. The mechanical equilibrium equation between the liquid bridge and the saw wires was established based on the Young-Laplace equation, and the theoretical model of the as-cut wafer thickness was derived during the sawing process. The effect of the saw wire tensioning force, span, the diameter of the core wire and the wetting angle of coolant on the as-cut wafer thickness variation was analyzed based on the model. The results show that the increase in the saw wire tensioning force, the core wire diameter and the wetting angle of coolant improved the thickness accuracy and reduced the thickness variation of the as-cut wafer. And the increase in the saw wire span reduced the thickness accuracy and increased the thickness variation. The research results of this paper provide the mechanism analysis for the thickness variation of the ultra-thin wafer during the slicing process. It is of great significance to produce the ultra-thin photovoltaic silicon wafers with the fine saw wire in the future.

Flexible pressure/temperature sensors with heterogeneous integration of ultra-thin silicon and polymer

Flexible pressure sensors and temperature sensors are widely used in various fields because of their advantages in high flexibility, good shape retention and extremely small thickness. However, it is quite challenging to fabricate ultra-thin flexible pressure sensors with reliable sensing performance. In this work, we propose a new type of silicon–polymer heterogeneously integrated MEMS flexible sensor with an ultra-thin silicon-based absolute pressure sensing element and a thermistor. In the study, a flexible MEMS fabrication process is developed, which enables simultaneous fabrication in two different substrates and self-release of the thin and slim flexible sensor. The front-end section of the flexible sensor is with the width as 125 μm, length as 3.2 cm and total thickness as 12 μm, where the integrated silicon substrate thickness is only 3 μm. The sensor takes a slender shape to allow for medical invasive measurement by inserting it into a slim medical catheter or a syringe needle-tube. The sensitivity of the fabricated ultra-thin absolute pressure sensor is tested as 45.2 μV kPa−1 under 3.3 V supplied voltage, with the nonlinearity as only ±0.16% FS. The sensitivity of the thermistor is 10.4 Ω °C−1 in the range of 0 °C–100 °C. Moreover, the polysilicon thermistor can also serve as a micro-heater, where an electric heating power of 107 μW results in a temperature increase of 13.5 °C. With ultra-thin slim structure and satisfactory performance, the MEMS flexible sensor is promising in various fields like biomedical applications.

An ultrathin triple‐band absorber for tuneable THz bio‐sensing

AbstractIn this paper, a multimode terahertz absorber is implemented using an ultrathin silicon ring with varying multimodal resonance. The rectangular silicon ring is providing three resonances with creating electromagnetic dipoles. The altering of these resonances is explicitly controlled with the help of a circular graphene ring. The graphene ring is used in the centre for tenability and to achieve perfect absorption. An equivalent circuit model is also presented and verified for the proposed structure. The design is intended to measure the glucose percentage in water. In addition, this can be used as a biosensor for the detection of malaria parasite percentage in water. A few important parameters like sensitivity and quality factors are considered to evaluate the performance of the said design. The sensitivity with analyte thickness is found to be 0.445 THz TU−1, 0.4255 THz TU−1, and 0.4305 THz TU−1. The corresponding quality factor is noted for the lower, middle, and upper bands as 235, 653, and 264 respectively. Further, the sensitivity and quality factors were measured just by changing the refractive index. The new estimated values are 0.480 THz RIU−1, 0.403 THz RIU−1, and 0.562 THz RIU−1 and corresponding quality factors are 203, 555, and 261 for lower, middle, and upper bands respectively. The design is also expected to flourish as a polarization‐insensitive absorber.

Single-nanowire-morphed mechanical slingshot for directional shooting delivery of micro-payloads

Stretching elastomer bands to accumulate strain energy, for a sudden projectile launching, has been an old hunting skill that will continue to find new applications in miniaturized worlds. In this work, we explore the use of highly resilient and geometry-tailored ultrathin crystalline silicon nanowires (SiNWs) as elastic medium to fabricate the first, and the smallest, mechanical slingshot. These NW-morphed slingshots were first grown on a planar surface, with desired layout, and then mounted upon standing pillar frames, with a unique self-hooking structure that allows for a facile and reliable assembly, loading and shooting maneuver of microsphere payloads. Impressively, the elastic spring design can help to store 10 times more strain energy into the NW springs, compared with the straight ones under the same pulling force, which has been strong enough to overcome the sticky van der Waals (vdW) force at the touching interfaces that otherwise will hinder a reliable releasing onto soft surface with low-surface energy or adhesion force, and to achieve a directional shooting delivery of precise amount of tiny payload units onto delicate target with the least impact damage. This NW-morphing construction strategy also provides a generic protocol/platform to fast design, prototype, and deploy new nanoelectromechanical and biological applications at extremely low costs.

Thin monolithic pixel sensors with fast operational amplifier output in a 65 nm imaging technology for ALICE ITS3

This work presents results on the Analog Pixel Test Structure (APTS), a 4 × 4 pixel matrix prototype equipped with an output buffer based on the fast individual operational amplifier (OPAMP) of analogue pixel signals to output pads for exploration of pixel timing performance. This work was part of the ALICE ITS3 upgrade and the CERN-EP R&D on monolithic sensors of the TPSCo 65-nm imaging technology. This upgrade will replace the inner layers of the ALICE Inner Tracking System at CERN with ultra-thin flexible wafer-scale monolithic silicon sensors. They will improve the material budget in this region, the tracking precision and the efficiency at low transverse momentum. This paper will show the gain of the signal chain in the APTS and its speed as a function of the configuration parameters, including calibration results with a 55Fe source. Two different pixel structures will be compared to demonstrate the possibility of enhancing the performance in terms of timing and charge collection efficiency by implant modifications in the epitaxial layer. Finally, test beam results planned at the Super Proton Synchrotron at CERN will provide full spatial and time resolution of the APTS OPAMP structures.

Ultracompact single-nanowire-morphed grippers driven by vectorial Lorentz forces for dexterous robotic manipulations

Ultracompact and soft pairwise grippers, capable of swift large-amplitude multi-dimensional maneuvering, are widely needed for high-precision manipulation, assembly and treatment of microscale objects. In this work, we demonstrate the simplest construction of such robotic structures, shaped via a single-nanowire-morphing and powered by geometry-tailored Lorentz vectorial forces. This has been accomplished via a designable folding growth of ultralong and ultrathin silicon NWs into single and nested omega-ring structures, which can then be suspended upon electrode frames and coated with silver metal layer to carry a passing current along geometry-tailored pathway. Within a magnetic field, the grippers can be driven by the Lorentz forces to demonstrate swift large-amplitude maneuvers of grasping, flapping and twisting of microscale objects, as well as high-frequency or even resonant vibrations to overcome sticky van de Waals forces in microscale for a reliable releasing of carried payloads. More sophisticated and functional teamwork of mutual alignment, precise passing and selective light-emitting-diode unit testing and installation were also successfully accomplished via pairwise gripper collaborations. This single-nanowire-morphing strategy provides an ideal platform to rapidly design, construct and prototype a wide range of advanced ultracompact nanorobotic, mechanical sensing and biological manipulation functionalities.

Arrays of Fresnel Nanosystems for Enhanced Photovoltaic Performance.

Omnidirectional broadband absorption of the solar radiation is pivotal to solar energy harvesting and particularly to low-cost non-tracking photovoltaic (PV) technologies. The current work numerically examines the utilization of surface arrays composed of Fresnel nanosystems (Fresnel arrays), which are reminiscent of the known Fresnel lenses, for the realization of ultra-thin silicon PV cells. Specifically, the optical and electrical performances of PV cells integrated with Fresnel arrays are compared with those of a PV cell incorporated with an optimized surface array of nanopillars (NP array). It is shown that the broadband absorption of specifically tailored Fresnel arrays can provide an enhancement of ∼20% over that of an optimized NP array. The performed analysis suggests that broadband absorption in ultra-thin films decorated with Fresnel arrays is driven by two light trapping mechanisms. The first is light trapping governed by light concentration, induced by the arrays, into the underlying substrates, which increases the optical coupling between the impinging illumination and the substrates. The second mechanism is light trapping motivated by refraction, as the Fresnel arrays induce lateral irradiance in the underlying substrates, which increases the optical interaction length and hence the overall probability for optical absorption. Finally, PV cells incorporated with surface Fresnel arrays are numerically calculated, with short-circuit current densities (Jsc) which are ∼50% higher than that of a PV cell incorporated with an optimized NP array. Also, the effect of increased surface area, due to the presence of Fresnel arrays, and its effect on surface recombination and open-circuit voltage (Voc) are discussed.

See‐Through Flexible Photovoltaic Modules of Ultrathin Silicon Solar Microcells Enhanced by Synergistic Luminescent and Reflective Near‐Infrared Backplanes

AbstractUltrathin single‐crystalline silicon solar microcells assembled into see‐through and flexible modules have exhibited broadly applicable cost‐effective photovoltaics with reliable durability and efficiency. However, their module output power has suffered from inherent limitations caused by the inferior photon absorption property and the inactive see‐through windows. Herein a strategy is presented to enhance the performance of see‐through flexible ultrathin silicon microcell modules by employing visibly transparent but near‐infrared‐manipulatable optical backplanes, such as a luminescent waveguide gathering near‐infrared photons and a backside reflector mitigating near‐infrared photon escape. Simultaneous integration of these near‐infrared backplanes provides more photovoltaic gains to silicon solar modules than the sum of each backplane capability, and this synergy is due to the promoted properties of the photoluminescence process and waveguiding. The experimental module with ≈3‐µm thick silicon solar microcells can achieve up to ≈40%‐boosted output power generation when assisted by these backplanes. Detailed studies of optical and photovoltaic characterizations for near‐infrared backplanes and their integration modules elucidate the effectiveness of designed backplanes for see‐through flexible silicon photovoltaics.

Plasmonic enhanced ultra-thin solar cell: A combined approach using fractal and nano-antenna structure to maximize absorption

In this study, a combined structure is proposed to develop ultra-thin silicon solar cells. This integrated structure consists of silver fractal-like nano-particles and leaky wave nanoantennas. The nano-cuboid pattern embedded inside anti-reflective coating benefits from different optical modes, such as surface plasmons and cavity modes, which trap more light and amplify the electric field in the upper region of the absorber layer. On the bottom side, the hybrid plasmonic mode in the structure of the optical nanoantenna makes it possible to focus and direct the incoming light on the bottom of the absorber layer and increase the optical pathlengths in the ultra-thin film solar cell. The nanoantenna behavior and three-dimensional finite-difference time-domain analysis show that photon absorptions improve significantly at long wavelength lightwaves through this proposed combined structure. The short circuit current enhancement of the solar cell under 1 sun standard illumination is obtained by a factor of 1.94 and 1.80 for TM and TE polarization of incident light, respectively. Due to the acceptable results for different incident angles and polarizations, ultra-thin thickness, and nano-cuboids synthesis feasibility, our structure has the potential to be applied in the design of miniaturized photovoltaic devices.

High-fidelity moulding growth and cross-section shaping of ultrathin monocrystalline silicon nanowires

Catalytic growth of ultrathin silicon nanowires (SiNWs) provides ideal 1D channel materials for the construction of high-performance field effect transistors, where the diameter, uniformity and crystalline qualities are of utmost importance. In this work, a high-fidelity moulding growth of orderly ultrathin monocrystalline SiNWs, with diameter of 17±2nm, has been accomplished within tightly confined nanogrooves. A continuous and deterministic groove-width-transition or squeezing strategy has also been developed to accomplish an effective cross-section tailoring of the as-grown SiNW channels, while enabling a close-to-unity growth filling rate within the guiding grooves. Finally, a size-dependent adatom-searching model is proposed to explain how a monocrystalline SiNWs can be obtained even at such a low growth temperature of < 350 ℃. These results indicate a feasible catalytic growth fabrication route to implement monolithic 3D integration of advanced in-memory-computing and neuromorphic electronics.

Ultrathin Crystalline Silicon Nano and Micro Membranes with High Areal Density for Low-Cost Flexible Electronics.

Ultrathin crystalline silicon is widely used as an active material for high-performance, flexible, and stretchable electronics, from simple passive and active components to complex integrated circuits, due to its excellent electrical and mechanical properties. However, in contrast to conventional silicon wafer-based devices, ultrathin crystalline silicon-based electronics require an expensive and rather complicated fabrication process. Although silicon-on-insulator (SOI) wafers are commonly used to obtain a single layer of crystalline silicon, they are costly and difficult to process. Therefore, as an alternative to SOI wafers-based thin layers, here, a simple transfer method is proposed for printing ultrathin multiple crystalline silicon sheets with thicknesses between 300nm to 13µm and high areal density (>90%) from a single mother wafer. Theoretically, the silicon nano/micro membrane can be generated until the mother wafer is completely consumed. In addition, the electronic applications of silicon membranes are successfully demonstrated through the fabrication of a flexible solar cell and flexible NMOS transistor arrays.

Ultrathin silicon wafer defect detection method based on IR micro-digital holography.

Ultrathin silicon wafers are key components of wearable electronic devices and flexible electronics. Defects produced during the preparation process of ultrathin silicon wafers have a great influence on the electronic performance. A high-precision, nondestructive, and rapid damage detection method is urgently needed. IR digital holography has the advantage of being insensitive to visible light and environmental interference. In addition, micro-holography can achieve micro-target scaling with large range scaling. An ultrathin silicon wafer defect detection method of IR micro-digital holography is proposed in this paper for what we believe is the first time. Using the proposed defect detection method based on holography, the detection accuracy reached the submicron level.