Guoli Li

Silicon-on-Insulator Photodiode on Micro-Hotplate Platform With Improved Responsivity and High-Temperature Application

This paper reports on the performance of a silicon-on-insulator photodiode suspended on a dielectric membrane. The micro-hotplate platform consists of a micro-heater and a thin-film lateral P+/P-/N+ (PIN) photodiode. Without optimizing the multilayer stack on top of the PIN diode, experimental responsivities of the suspended photodiodes at room temperature (RT) are 0.02-0.06/W within the visible and near the IR light range, under a reverse bias of -2 V. Up to 2.5×, responsivity improvement has been achieved with regard to the diodes on the substrate thanks to reflection from the gold finish layer of the device package acting as a bottom mirror. Optimizing the layer stack above the diode, the responsivity of the on-membrane device can be theoretically improved up to 0.09-0.11 A/W within 450-520-nm wavelength range. Measured from RT up to 200 °C, the photodiodes on membrane continuously show an improved optical response under high-power LED illumination. Assisted by the micro-heater as heat source, the suspended photodiode can work stably up to 200 °C with in situ temperature sensing and control, which makes it highly suitable and attractive for high-temperature application. Full 2-D ATLAS device simulations have been comprehensively performed to investigate the optical and electrical characteristics. Very good agreement has been achieved between the numerical simulations and the experimental data.

Wide band study of silicon-on-insulator photodiodes on suspended micro-hotplates platforms

In this paper, the performances of a lateral thin-film PIN photodiode based on silicon-on-insulator technology are reported for applications from blue to red wavelengths. The platform consists of a micro-hotplate with a suspended heater and a photodiode. Responsivities of 0.01 to 0.05 A/W were obtained for 450-900 nm light range in reverse bias operation. Suspended photodiodes give up to 5x responsivity improvement with regard to the photodiodes on substrate. In addition to photodetection, the diode can monitor the temperature with a linear voltage decreasing by about 1.4 mV/K, under 50 μA constant forward current for a large range of temperature (measured from 25 to 300°C).

Operation of suspended lateral SOI PIN photodiode with aluminum back gate

In this paper, we report a lateral silicon-on-insulator (SOI) P+P-N+ (PIN) photodiode suspended on a micro-hotplate platform, with aluminum (Al) layer deposited on backside. Voltage applied to the Al back gate can modify the depletion condition in the intrinsic (I) region. The device output photocurrent reaches a maximum under fully-depleted (FD) condition achieved by the positive back-gate bias. Moreover, the backside Al acts as a excellent reflector, which for specific wavelength ranges (around 500, 600, 770 nm) significantly boosts optical response of the SOI PIN photodiode. Over 2~3× improvements of responsivity (up to R = 0.1 A/W at 590 nm) have been achieved and validated in the measurements at 490, 590, 760 nm. Full optoelectronic two-dimensional (2-D) device simulations are conducted in Atlas software to comprehensively validate the device performance and improvement.

Multiple-Wavelength Detection in SOI Lateral PIN Diodes With Backside Reflectors

This research details the potential of a microhotplate photo sensor, based on a silicon-on-insulator (SOI) lateral PIN (P+/P–/N+) diode and a microheater, fabricated on a thin suspended membrane from a commercial 1.0-μm SOI complementary metal oxide semiconductor technology. A local annealing (30-min. microheating, at elevated temperature ∼250 °C) is directly carried out onto the suspended diode to optimize device characteristics (e.g., leakage current, output optical response), for device long-term stability and industrial application. The optical performances of such SOI lateral PIN diodes with four different backside reflectors placed below them are fully investigated. Under same incident illumination, four specific output photocurrents and responsivities are therefore obtained due to the varied light absorption in the active Si film. By combining the photodiodes responses with the four backside reflectors (i.e., gold, aluminum, silicon substrate, and black silicon), multiple-wavelength detection can be straightforwardly achieved within the 450–900-nm wavelength range, which makes the SOI photodiode highly promising in red-green-blue sensing, gas analyzing or plasma monitoring applications.

Understanding hydrogen and nitrogen doping on active defects in amorphous In-Ga-Zn-O thin film transistors

This work analyses the physics of active trap states impacted by hydrogen (H) and nitrogen (N) dopings in amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) and investigates their effects on the device performances under back-gate biasing. Based on numerical simulation and interpretation of the device transfer characteristics, it is concluded that the interface and bulk tail states, as well as the 2+ charge states (i.e., acceptors VO2+) related to oxygen vacancy (VO), are neutralized by the H/N dopants incorporation via an experimental plasma treatment. Moreover, the simulation reveals that an acceptor-like defect VOH has been induced by the H doping, to support the observed additional degradation of device subthreshold slope. Superior stability of the optimized a-IGZO TFTs under a proper amount of H/N doping is demonstrated by the decreased density of VO-related defects in simulation, where hole (VO0 donor) and electron trapping (Oi acceptor) occurs during the negative or positive bias stresses. This work benefit lies in an in-depth systematic understanding and exploration of the effects of the incorporation of the H and N dopants into the a-IGZO film for the TFTs improvement and optimization.This work analyses the physics of active trap states impacted by hydrogen (H) and nitrogen (N) dopings in amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) and investigates their effects on the device performances under back-gate biasing. Based on numerical simulation and interpretation of the device transfer characteristics, it is concluded that the interface and bulk tail states, as well as the 2+ charge states (i.e., acceptors VO2+) related to oxygen vacancy (VO), are neutralized by the H/N dopants incorporation via an experimental plasma treatment. Moreover, the simulation reveals that an acceptor-like defect VOH has been induced by the H doping, to support the observed additional degradation of device subthreshold slope. Superior stability of the optimized a-IGZO TFTs under a proper amount of H/N doping is demonstrated by the decreased density of VO-related defects in simulation, where hole (VO0 donor) and electron trapping (Oi acceptor) occurs during the negative or positive bias stresses. ...

Leakage Current and Low-Frequency Noise Analysis and Reduction in a Suspended SOI Lateral p-i-n Diode

In this paper, we present a detailed analysis of leakage current in a silicon-on-insulator (SOI) lateral P+P−N+ (p-i-n) diode suspended on a microheating platform, combining device experimental characterization and numerical simulation. The diode leakage currents have been extensively studied using the back-gate bias as a means to alter the space-charge (SC) condition at the P− region (I-region)/buried oxide interface from accumulation to full depletion, and finally to inversion. Both dark leakage current analysis and low-frequency noise characterization performed on the suspended SOI lateral p-i-n diode indicate device degradation induced by microelectromechanical systems postprocessing (i.e., deep reactive-ion etching or aluminum deposition). A low-temperature (~250 °C) in situ (i.e., using embedded microheater) annealing of SOI lateral p-i-n diode after postprocessing allows reduction of the diode leakage current and optimization of the device performance by neutralizing the interface traps and improving carriers’ lifetime and surface recombination velocity. Numerical simulations have been performed with Atlas/SILVACO for deeper analysis of the leakage current behavior in the lateral p-i-n diode and identification of the generation mechanism dominating the diode leakage behavior. Simulation reveals that the dominant generation rate in the diode depends on the SC conditions, the interface trap density, and the carriers’ lifetime in the I-region. The experimental and simulated behaviors of “as processed” and annealed diode leakage current are shown to be in good qualitative agreement.

A 3D space coiling metamaterial with isotropic negative acoustic properties

We design a 3D acoustic metamaterial having a coiling resonant structure with high symmetry. Eigenstate analysis reveals that such a 3D metamaterial has two significant Mie-type eigenmodes, monopole and dipolar resonances. Large blocking of sound waves in the low-frequency range between monopole and dipolar resonances is observed numerically and experimentally. The effective properties extracted from the reflection and transmission coefficients show negative bulk modulus around the monopole resonant frequency and negative mass density around the dipolar resonant frequency. By employing the proposed two-scale model, the metamaterial system demonstrates the functionalities of sound cloaking and super-tunneling within a finite space.