Silicon Microdisplay Research Articles

Preview the Products on Display at Display Week 2023

Preview the Products on Display at Display Week 2023

Analysis of a vertically aligned liquid-crystal on silicon microdisplay for photonics applications

We present the characterization results for an analogically addressed vertically aligned liquid crystal on silicon microdisplay (VA-LCoS). We show that it covers more than 360º phase modulation range at 1550 nm, and that in the visible the range available enables the generation of multiorder DOEs. There are basically no studies dealing with the characterization of vertically aligned high resolution LCoS devices, since the ones typically found in the literature and commercially available correspond to the parallel aligned. We have also verified that the microdisplay used in this work is free from flicker, which is a very interesting feature for application where the phase stability is of the utmost importance. The results shown here represent a first step in the work underway oriented to the generation of programmable DOEs for telecommunication applications (C-band) and for the visible spectrum.

Polarimetric analysis of cross-talk phenomena induced by the pixelation in PA-LCoS devices

Liquid crystal on silicon (LCoS) microdisplays are an element commonly found in advanced photonic applications. Phase-only modulation and spatial light modulators (SLMs) use parallel-aligned LCoS (PA-LCoS) microdisplays due to their large resolution and small pixel size. However, the crosstalk between neighbouring pixels induces several phenomena, i.e. the smoothing of the electric field in the interpixel region known as fringing fields, out-of-plane reorientation of the liquid crystal director, and diffraction effects due to the finite pixel grid pattern. These effects degrade the performance in SLM applications. Therefore, a rigorous numerical analysis is carried out based on a full 3D model that estimates the LC director distribution of the PA-LCoS microdisplay through uniform applied voltages. Once the LC director distribution is known, a numerical finite-difference scheme simulates light propagation across the structure. Here, the impact of crosstalk is analysed from the polarimetric point of view for different pixel and interpixel sizes. It has been found that the finite-patterned pixel scheme induces the phenomena previously addressed, degrading the responses of the Stokes vector components S0, and S1 and also the degree of polarization (DOP). Furthermore, the impact over these parameters is generally inversely proportional to the fill factor. To isolate the influence of diffraction, out-of-plane, and fringing fields effects is challenging since all phenomena are mixed in both time and space, however we have found some useful trends.

All Silicon Microdisplay Fabricated Utilizing 0.18 μm CMOS-IC With Monolithic Integration

A low voltage all silicon microdisplay is presented based on MOS-like gate-control all-Silicon light-emitting diode (LED) in standard 0.18 μm complementary metal oxide semiconductor (CMOS) technology. The MOS-like LED is designed under a PN alternate structure with polysilicon gate control electrode for high luminous intensity and low operating voltage. The microdisplay device is fabricated based on the LED as pixel units. The size of the proposed microdisplay device is 6.2 mm × 5.0 mm with a about 368 mW/mm2 luminous intensity at the stable operating voltage of 1.8 V.

Unitary matrix approach for a precise voltage dependent characterization of reflective liquid crystal devices by average Stokes polarimetry

Precise characterization of parallel-aligned liquid crystal on silicon microdisplays has an important impact in many advanced photonics applications. We show liquid crystal on silicon (LCoS) modeled as a non-absorbent reciprocal device. Combined with time-average Stokes polarimetry, LCoS enables us to demonstrate robust measurements across the whole applied voltage range for the retardance and its flicker, and also as a novelty for the director orientation. We obtain that the director orientation changes across the voltage range, especially at larger applied voltages. This is a small effect, but it may provide a deeper insight into the internal dynamics in the liquid crystal layer, and in sensitive phase-only applications will produce a coupling between amplitude and phase.

A Pixel Circuit With Wide Data Voltage Range for OLEDoS Microdisplays With High Uniformity

A new pixel circuit is proposed for the realization of high resolution and high uniformity organic light-emitting diode on silicon (OLEDoS) microdisplays in this article. A compensation scheme is adopted to mitigate the influence of threshold voltage variation of the driving transistor on display uniformity. Furthermore, two coupling capacitors are used to reduce the voltage at the gate terminal of the driving transistor in order to extend the data voltage range. The performance of the proposed pixel circuit is verified in an industrial 0.18- $\mu \text{m}$ CMOS process. Simulation results show that the data voltage of the proposed pixel circuit ranges from 0.5 to 3.12 V, which is up to $4.37\times $ wider than the previously published pixel circuits. The emission current error of the proposed pixel circuit varies from −2.1% to 2.08%, under the condition of ±5 mV threshold voltage variation for the driving transistor. The maximum emission current error changes from −10.36% to −2.62% when the OLED turn-on voltage is increased by 5 to 20 mV due to device aging. Furthermore, the proposed pixel circuit only occupies a layout area of $8.1\,\,\mu \text{m}\,\,\times {4}\,\,\mu \text{m}$ .

Anamorphic and Local Characterization of a Holographic Data Storage System with a Liquid-Crystal on Silicon Microdisplay as Data Pager

In this paper, we present a method to characterize a complete optical Holographic Data Storage System (HDSS), where we identify the elements that limit the capacity to register and restore the information introduced by means of a Liquid Cristal on Silicon (LCoS) microdisplay as the data pager. In the literature, it has been shown that LCoS exhibits an anamorphic and frequency dependent effect when periodic optical elements are addressed to LCoS microdisplays in diffractive optics applications. We tested whether this effect is still relevant in the application to HDSS, where non-periodic binary elements are applied, as it is the case in binary data pages codified by Binary Intensity Modulation (BIM). To test the limits in storage data density and in spatial bandwidth of the HDSS, we used anamorphic patterns with different resolutions. We analyzed the performance of the microdisplay in situ using figures of merit adapted to HDSS. A local characterization across the aperture of the system was also demonstrated with our proposed methodology, which results in an estimation of the illumination uniformity and the contrast generated by the LCoS. We show the extent of the increase in the Bit Error Rate (BER) when introducing a photopolymer as the recording material, thus all the important elements in a HDSS are considered in the characterization methodology demonstrated in this paper.

Design of Diffraction Limited Head Mounted Display Optical System Based on High Efficiency Diffractive Elements

A diffraction limited optical system for head mounted displays (HMDs) was designed. This optical system consists of four modules, including 1:5 mm and 5:30 mm beam expanders, polarization grating-polarization conversion system (PG-PCS) and refractive/diffractive projection optical module. The PG-PCS module transforms the unpolarized Gaussian beam to a linearly polarized beam and it simultaneously homogenizes the spatial intensity profile. The optical projector module has a 30° field of view, a 22 mm eye relief, and a 10 mm exit pupil diameter with a compact structure. Common acrylic materials were utilized in the optical design process; therefore, the final optical system was lightweight. The whole optical system is suitable for a 0.7 inch liquid crystal on silicon microdisplay (LCOS) with HDTV resolution (1920×1080) and 8.0 μm pixel pitch.

A 2822-ppi Resolution Pixel Circuit With High Luminance Uniformity for OLED Microdisplays

In this paper, a pixel circuit comprising four p-channel mosfet s and one capacitor is proposed for a high-resolution organic light emitting diode on silicon microdisplays with high luminance uniformity. The proposed pixel circuit improves the luminance uniformity by compensating for the threshold voltage $\rm{(V}_{\rm{th}}\rm{)}$ variation of the driving transistors. In addition, it extends the data voltage range to precisely control the emission current $\rm{(I}_{\rm{em}}\rm{)}$ . The test pattern of the proposed pixel circuit is fabricated on a single-crystalline silicon wafer as a backplane using a 90 nm CMOS process and occupies a subpixel area of 3 μ m × 9 μ m, corresponding to a resolution of 2822 pixels per inch. To verify the performance of the proposed pixel circuit, $\rm{I}_{\rm{em}}$ is measured from 24 fabricated test patterns. When the $\rm{V}_{\rm{th}}$ variation is not compensated for, the deviation of the measured $\rm{I}_{\rm{em}}$ ranges from –17.48% to +14.40% with a deviation of $\rm{V}_{\rm{th}}$ from –7.19 mV to +7.19 mV. On the other hand, when the $\rm{V}_{\rm{th}}$ variation is compensated for, the deviation of the measured Iem only ranges from –1.63% to +1.15%. Moreover, the proposed pixel circuit extends the data voltage range up to 1.289 V, which is 1.81 times wider than the source-to-gate voltage of the driving transistor which generates the maximum $\rm{I}_{\rm{em}}$ . In addition, the maximum organic light-emitting diode luminance of the proposed pixel circuit is constantly maintained between 292.5 and 303.8 cd/m 2 in the temperature range of –45 °C to 60 °C.

GaN-based LED micro-displays for wearable applications

LED micro-displays offer diverse applications with their superior characteristics and unique performance, particularly in high light utilization efficiency (LUE), design simplicity, long lifetime, and excellent visibility under bright day-light. In this work, we designed and fabricated GaN-based light emitting diode on silicon (LEDoS) micro-displays by integrating monolithic LED micro-arrays and active matrix substrates using flip-chip technology. The LEDoS micro-displays have been developed in generations with increasing display resolutions and scaled pixel pitches. Representative display images have been demonstrated and show great potential in wearable electronic and photonic applications.

Exploring binary and ternary modulations on a PA-LCoS device for holographic data storage in a PVA/AA photopolymer.

We focus on the novelty of three elements in holographic data storage systems (HDSS): the data pager, where we introduce a parallel-aligned liquid crystal on silicon (PA-LCoS) microdisplay; the recording material, where we consider the highly versatile PVA/AA photopolymer; and also in the architecture of the object arm, where a convergent correlator system is introduced. We show that PA-LCoS devices cannot implement pure hybrid-ternary modulated (HTM) data pages but a rather close approximation. Validation of the HDSS expressions for the convergent correlator and comparison with the widespread 4-f system is performed. Experimental results with PVA/AA material showing bit-error rates (BER) in the range of 10-3, further show its potential application for HDSS, and also demonstrate the validity of the testing platform and PA-LCoS calibration and optimization.

Predictive capability of average Stokes polarimetry for simulation of phase multilevel elements onto LCoS devices.

Parallel-aligned (PA) liquid-crystal on silicon (LCoS) microdisplays are especially appealing in a wide range of spatial light modulation applications since they enable phase-only operation. Recently we proposed a novel polarimetric method, based on Stokes polarimetry, enabling the characterization of their linear retardance and the magnitude of their associated phase fluctuations or flicker, exhibited by many LCoS devices. In this work we apply the calibrated values obtained with this technique to show their capability to predict the performance of spatially varying phase multilevel elements displayed onto the PA-LCoS device. Specifically we address a series of multilevel phase blazed gratings. We analyze both their average diffraction efficiency ("static" analysis) and its associated time fluctuation ("dynamic" analysis). Two different electrical configuration files with different degrees of flicker are applied in order to evaluate the actual influence of flicker on the expected performance of the diffractive optical elements addressed. We obtain a good agreement between simulation and experiment, thus demonstrating the predictive capability of the calibration provided by the average Stokes polarimetric technique. Additionally, it is obtained that for electrical configurations with less than 30° amplitude for the flicker retardance, they may not influence the performance of the blazed gratings. In general, we demonstrate that the influence of flicker greatly diminishes when the number of quantization levels in the optical element increases.

A Novel BLU-Free Full-Color LED Projector Using LED on Silicon Micro-Displays

In this letter, we have described the design and fabrication of a novel backlight-unit (BLU)-free full-color light emitting diode (LED) based projector. The prototype used three active matrix addressable light emitting diode on silicon (LEDoS) micro-displays with peak emission wavelengths of 630, 535, and 445 nm. The LEDoS micro-displays were realized by integrating monolithic micro-LED arrays and silicon-based integrated circuits using a flip-chip bonding technique. Since the LEDoS micro-displays are self-emitting, conventional BLUs used in liquid crystal displays were not needed. Using a trichroic prism to combine the light from the three LEDoS chips, we have produced the world's first three-LEDoS projector. This BLU-free three-LEDoS projector consists of much fewer optical components and has significantly higher light utilization efficiency compared with conventional projectors.

360 PPI Flip-Chip Mounted Active Matrix Addressable Light Emitting Diode on Silicon (LEDoS) Micro-Displays

In this paper, we describe the design and fabrication of 360 PPI flip-chip mounted active matrix (AM) addressable light emitting diode on silicon (LEDoS) micro-displays. The LEDoS micro-displays are self-emitting devices which have higher light efficiency than liquid crystal based displays (LCDs) and longer lifetime than organic light emitting diodes (OLEDs) based displays . The LEDoS micro-displays were realized by integrating monolithic LED micro-arrays and silicon-based integrated circuit using a flip-chip bonding technique. The active matrix driving scheme was designed on the silicon to provide sufficient driving current and individual controllability of each LED pixel. Red, green, blue and Ultraviolet (UV) LEDoS micro-displays with a pixel size of 50 μm and pixel pitch of 70 μm were demonstrated. With a peripheral driving board, the LEDoS micro-display panels were programmed to show representative images and animations.

60.4: A Novel Full‐Color 3LED Projection System using R‐G‐B Light Emitting Diodes on Silicon (LEDoS) Micro‐displays

AbstractR‐G‐B light emitting diode on silicon (LEDoS) micro‐displays were fabricated and the world's first full color 3LED projection prototype is presented. LEDoS micro‐displays were realized by flip‐chip bonding of LED micro‐arrays on silicon CMOS active‐matrix drivers. Using trichroic prism, images generated from three self‐emissive R‐G‐B LEDoS micro‐displays were combined to form a color image, demonstrating great potential for high efficiency and high brightness projection applications.

Digital High Resolution Small Pixel LCOS Technology

The progress in digital high resolution, small pixel liquid crystal on silicon (LCOS) microdisplays will be discussed and how it will lead to HD displays in very small form factors. The first generation of this technology is enabling very small yet high resolution projection engines devices that can be embedded in cell phones, cameras, head-mount displays, and set-top boxes and the next generation will bring HD resolution. As lasers become more affordable we see this LCOS display technology fundamentally changing the power consumption, cost, and size of pico-projectors and other display devices. One of the most interesting conclusions is that by using LCOS technology in combination with lasers, it should soon be possible to build an “ultra-green” television that would consume less than 1/8th the power of equivalent size LCD flat panel TV.

Three-dimensional optical analyses and optimizations of a vertical alignment color-filters-embedded liquid-crystal-on-silicon microdisplay

The process of vertical alignment (VA) mode color filter liquid crystal on silicon (CF-LCoS) microdisplay was developed. In order to minimize the fringing field effect in small color pixels, a three dimensional (3D) optical model was established and performed to analyze this VA mode CF-LCoS microdisplay. The simulated result was compared with the experimental data and they coincided well. Optimization of this breed of VA mode CF-LCoS microdisplay was proposed with optimal pretilt angle and pixel size. With the pretilt angle of 86 degrees and the pixel size of 15 μm, the color purity of the VA mode CF-LCoS microdisplay could attain more than 60% National Television Standards Committee (NTSC) level, and the contrast was larger than 400.

High speed liquid crystal over silicon display based on the flexoelectro-optic effect

One of the key technologies to evolve in the displays market in recent years is liquid crystal over silicon (LCOS) microdisplays. Traditional LCOS devices and applications such as rear projection televisions, have been based on intensity modulation electro-optical effects, however, recent developments have shown that multi-level phase modulation from these devices is extremely sought after for applications such as holographic projectors, optical correlators and adaptive optics. Here, we propose alternative device geometry based on the flexoelectric-optic effect in a chiral nematic liquid crystal. This device is capable of delivering a multilevel phase shift at response times less than 100 microsec which has been verified by phase shift interferometry using an LCOS test device. The flexoelectric on silicon device, due to its remarkable characteristics, enables the next generation of holographic devices to be realized.

Study of assembly processes for liquid crystal on silicon (LCoS) microdisplays

This paper involves the development of two critical assembly processes for liquid crystal on silicon (LCoS) microdisplays. The processes investigated include the lamination of cover glass on silicon and a LC filling process. For the lamination process, a tool and process were designed and developed with the objective to attach the cover glass on a silicon die and achieve a cell gap of 3-/spl mu/m between them. The gap was achieved and verified with various measurement techniques. The lamination process involved the deposition of an adhesive ring and subsequently squeezing the two parallel plates until the desired cell gap was achieved. An analytical model was developed to estimate the time required to achieve a 3-/spl mu/m cell gap by applying different pressures on the cover glass. The analytical model proved to be a guideline in developing the lamination process. The second process in the assembly is filling the cavity between the cover glass and silicon with LC material. For LC filling, a tool was designed and process was developed. The process works on the principle of flow of fluid in a capillary. The flow rate was enhanced by applying a vacuum to the cavity. An analytical model was developed to estimate the time needed to fill the 3-/spl mu/m wide cavity. Fill time is a function of gap width between glass and silicon, pressure applied within the cavity, cavity length and the viscosity of the LC material.

Application of Photoalignment Technology to Liquid-Crystal-on-Silicon Microdisplays

We applied photoalignment technology to liquid-crystal-on-silicon microdisplays and characterized their performance. A three-step photoexposure method was developed to solve problems with alignment disturbances on reflective silicon panels. The azimuthal and polar anchoring energies of photoalignment layers produced by this method were high and comparable with that of rubbed polyimide layers. We assembled both the rubbed and photoaligned microdisplays on a MTN 90° configuration for characterization and comparison. These two kinds of silicon microdisplays had good and comparable characteristics in terms of contrast, response time, voltage holding ratio and residual DC charge. The rubbed microdisplays were more uniform, which we attributed to a more mature fabrication technology, while the photoaligned microdisplays had far fewer defects due to the noncontact nature of the photoalignment technology.