Semiconductor Energy Laboratory (Japan)

In this study, we designed and fabricated a crystal InOx‐based transistor on a 3.5th generation glass (600 mm × 720 mm) substrate line. The transistor exhibits high field‐effect mobility around 100 m 2 /Vs, an on‐state current higher than that of a low‐ temperature polysilicon‐based transistor, normally‐off characteristics, and high reliability. By combining our organic light‐emitting diode (OLED) patterning technology, we obtained an 8K4K OLED display with high luminance and low power consumption.

The recombination region in a light‐emitting layer in a blue phosphorescent organic light‐emitting diode (OLED) was controlled through spontaneous orientation polarization in an electron‐transport layer. We developed a blue phosphor‐sensitized OLED using a fluorescent material whose quenching due to Dexter energy transfer is inhibited. A high‐luminance and high‐reliability tandem OLED employing both technologies was achieved.

Abstract We have developed an integration process for LED microdisplays toward augmented reality (AR) applications and present the first demonstration of a blue mono‐color active‐matrix LED microdisplay fabricated with this process methodology. One of the primary manufacturing challenges in realizing LED microdisplays is to develop a process that provides pixel‐level heterogeneous connections between III‐V compound LEDs and Si CMOS circuits at a fine pixel pitch. In this work, a die‐to‐silicon process is employed, in which GaN on Si chips are reconstituted on a larger‐diameter support Si wafer (referred to as GaN/Si wafer), allowing the use of Si CMOS wafer processes, including novel Cu‐Cu hybridization. After the Cu‐Cu hybridization process to bond a die‐to‐silicon transferred GaN/Si wafer and a Si CMOS backplane wafer, LED mesas and on‐chip lenses (OCLs) are fabricated. We achieved high yields of pixel‐level connections at 3.8‐μm and 4.5‐μm pitches through the Cu‐Cu hybridization. Finely tapered 1.2‐μm LED mesas with OCLs exhibited a 4.2‐fold enhancement in light extraction efficiency (LEE) compared with a Lambertian emitter within the emission angle of ±20°. Also, we introduce the key features and results of the prototyped 0.26‐in., 5,644‐ppi LED microdisplay.

This work introduces a probabilistic numerical simulation method to describe or predict the spherulitic morphology of semicrystalline polymer formed during non-isothermal crystallization process. The numerical simulation is based on the general crystallization theory, which consists of random nucleation and subsequent growth of supermolecular formations. The model is capable for prediction of morphology from the conversion curve of crystallization recorded by calorimetry during crystallization at a constant cooling rate. Samples made of polypropylene nucleated by different nucleating agents were used as a model material for testing the simulation approach. The results indicated that valuable structural information can be predicted from the conversion curve, like nucleus density, average spherulite size and size distribution as well. In addition, the simulation method also capable to predict the mechanism of nucleation during the crystallization process, namely, whether the number of nuclei is constant or continuously changing. The results also indicated that nucleus density increases significantly as a consequence of heterogeneous nucleation, which indicates that the simulation results in realistic and reliable structural data both in nucleated and non-nucleated samples.

Formation of a single crystalline oxide semiconductor on an insulating film as a channel material capable of three-dimensional (3D) stacking would enable 3D very-large-scale integration circuits. This study presents a technique for forming single-crystalline In2O3 having no grain boundaries in a channel formation region on an insulating film using the (001) plane of c-axis-aligned crystalline indium gallium zinc oxide as a seed. Vertical field-effect transistors using the single-crystalline In2O3 had an off-state current of 10−21 A μm−1 and electrical characteristics were improved compared with those using non-single-crystalline In2O3: the subthreshold slope was improved from 95.7 to 86.7 mV dec.−1, the threshold voltage showing normally-off characteristics (0.10 V) was obtained, the threshold voltage standard deviation was improved from 0.11 to 0.05 V, the on-state current was improved from 22.5 to 28.8 μA, and a 17-digit on/off ratio was obtained at 27 °C.

LiCoO2 is a historic lithium-ion battery cathode that continues to be used today because of its high energy density. However, the practical capacity of LiCoO2 is limited owing to the harmful phase transition at high voltages, which prevents the realization of its theoretical capacity. Here, we treat LiCoO2 particles with a molten salt of MgF2–LiF as a reaction accelerator to facilitate the diffusion and doping of magnesium into bulk LiCoO2 and to form a stable coating layer on the particle surface. Ex situ X-ray diffraction analysis confirms the inhibition of the harmful phase transition and the emergence of a different phase as the modified LiCoO2 was charged up to 4.7 V. The modified LiCoO2 shows high electrochemical performance during high-voltage operation. This technology provides a guideline for the suppressing fundamental degradation associated with phase transition and achieving ultra-high energy density LiCoO2 cathodes.

Abstract We achieved a high‐luminance and highly reliable tandem organic light‐emitting diode (OLED) designed for photolithography applications by developing a new intermediate connector with high resistance to water and atmospheric elements. We succeeded in fabricating a red, green, and blue (RGB) side‐by‐side (SBS) tandem OLED display without a fine metal mask using our SBS pixel‐patterning method involving organic layer etching via photolithography.

Silicon epitaxy is an essential building block in the manufacturing of complementary metal-oxide semiconductor (CMOS) devices. Accurate determination of epitaxial layer thickness is indispensable for a uniform and reproducible process. In this paper, we compare thickness values of the transition zone in silicon epitaxial wafers obtained by two of Semilab’s production-compatible electrical and optical characterization techniques: Fourier-transform infrared (FTIR) reflectometry and spreading resistance profiling (SRP). We demonstrate a high correlation between transition zone thicknesses obtained from the optical modelling of FTIR reflectance spectra and SRP profiles. The dependance of transition zone thickness change on the high-temperature annealing steps is also examined. FTIR reflectometry thus offers a quick, contactless alternative for obtaining structural parameters of an epitaxial layer, and these values can be well matched to those given by SRP.

We prototyped a true analog current computing multilayer neural network (NN) chip, where multiple analog in-memory computing (AiMC) circuit blocks are connected to each other via simple analog non-linear operation circuits. The true analog current computing is achieved with the invention of an analog current rectified linear unit (ReLU) circuit of a three-stage current mirror. With the prototyped NN chip, we demonstrated that the true analog computing (1) achieves process variation compensation utilizing current driving, (2) eliminates digital-analog or analog-digital data conversion between NNs, and (3) realizes low power inference, not only in multiply-accumulate (MAC) but in ReLU operation. Through classification of Mixed National Institute of Standards and Technology dataset, the chip exhibits a low energy of 1.1 nJ/classification and an accuracy of 91.6%, achieves weight retention of five hours, much longer than dynamic random access memory, and enables 68% power reduction compared with serially connected two single-layer NN chips with analog-digital converters and digital-analog converters in between. Although periodic refresh from an external storage class memory is necessary for applications that require continuous operation exceeding five hours, our AiMC capable of MAC and non-linear operations with low power is effective in applications such as edge artificial intelligence terminals with limited power sources.

We fabricated a 1.50‐inch, 3207‐ppi OLED microdisplay with an oxide semiconductor LSI/silicon LSI backplane and a novel pancake lens. Patterning an OLED layer by lithography allows fabrication of an ideal display having low power consumption, an ultra‐high aperture ratio and a wide color gamut.