Miniaturized III-Nitride Asymmetric Optical link for the Monitoring of Vascular Heart Rate and Cardiac-Related Pulse Activity

/pdf/fully-implantable-retinal-prosthesis-chip-with-photodetector-4wsc4g7jsq.pdf

Fully Implantable Retinal Prosthesis Chip with Photodetector and Stimulus Current Generator

A new flexible trans-nail photoplethysmographic (PPG) sensor system is proposed and characterized from both aspects of mechanical and electrical properties in this study. The unique FHE (flexible hybrid electronics) structure is consisting of an elastomer as a flexible substrate in which Si LSI dielets having photodiode and LED driver circuits etc. are embedded based on a FOWLP concept. Stress buffer layers (SBLs) as a key material are inserted between interdielet wirings and the substrate to mitigate mechanical stress and enhance wire reliability. The impact of the Young's moduli of the SBLs on the repeated bendability of the FHE systems is described. In addition, we evaluate the electrical properties of the photodiode circuits between before and after bending for comparison.

Mechanical and Electrical Characterization of FOWLP-Based Flexible Hybrid Electronics (FHE) for Biomedical Sensor Application

Typical die shift is beyond several tens micrometers or more, which is a serious problem on advanced fan-out wafer-level packaging (FOWLP), to give inevitable misalignment errors in the subsequent photolithography processes for fine-pitch redistributed wiring layer (RDL) formation. In particular, this problem is expected to grow all the more serious in chiplets and tiny dies less than 1 mm in a side. In this work, the use of an anchoring layer is proposed to fix these dies/chiplets on a double-side laminate thermo-release tape and drastically reduce the die shift. In addition, an on-nail photoplethysmogram (PPG) sensor module as a part of flexible hybrid electronics (FHE) is integrated with $\mu $ LED ( $270\,\,\mu \text{m}\,\,\times 270\,\,\mu \text{m}$ ) based on a die-first FOWLP methodology using a biocompatible polydimethylsiloxane (PDMS) mold resin for real-time monitoring pulse wave and percutaneous oxygen saturation (SpO2). The repeated bendability of fan-out Au wirings formed on the PDMS and the current–voltage ( $I$ – $V$ ) behavior of the $\mu $ LED before and after die embedment in the PDMS is characterized.

/pdf/significant-die-shift-reduction-and-m-led-integration-based-gkzv93fz54.pdf

Significant Die-Shift Reduction and μ LED Integration Based on Die-First Fan-Out Wafer-Level Packaging for Flexible Hybrid Electronics

A good habit of measuring blood pressure (BP) daily is helpful for us to stay healthy or to monitor hypertensive conditions. However, the conventional method of measuring BP using a pressure cuff has many weaknesses. In order to eliminate the use of this pressure cuff, we proposed a system using the pulse arrival time (PAT) to measure BP. This PAT can be measured using time difference between the R-peaks of electrocardiogram (ECG) and photoplethysmography (PPG) signals. In our system, we obtained these two signals by using our self-designed ECG and PPG sensors. Our sensors were fabricated in 0.18 μm CMOS technology with a small recording area of about 2.53 mm2and 6.25 mm2, respectively. Our ECG sensor has variable amplifying gains and can achieve a total maximum gain of 60 dB. Besides that, it has a high pass filter with wide cutoff frequencies between 0.1-200 Hz, and low pass filter with cutoff frequencies of 0.2-10 kHz. The design of our ECG circuit allows us to obtain the ECG signals using fingertips and without using a ground electrode. This compact system has the potential to become a wireless wearable in the future. The measured PAT was fitted into a mathematical model and cuff-less BP readings were obtained. A plot of reference BP using oscillometric cuff and cuff-less BP showed a good correlation of r = 0.83 for systolic blood pressure (SBP). The SBP and diastolic blood pressure (DBP) mean absolute difference for the system are 6.75 mmHg and 6.08 mmHg respectively, which fairly passed the strict standard set by IEEE. In the future, our system will be compared with the use of sphygmomanometer, which is the gold standard, to further evaluate its accuracies.

Continuous Peripheral Blood Pressure Measurement with ECG and PPG Signals at Fingertips

Health monitoring and self-management have become increasingly more important because of health awareness improvement, the aging of population, and other reasons. In general, pulse waves are among the most useful physiological signals that can be used to calculate several parameters such as heart rate and blood pressure for health monitoring and self-management. To realize an automatic and real-time pulse-wave monitoring system that can be used in daily life, we have proposed a trans-nail pulse-wave monitoring system that was placed on the fingernail to detect photoplethysmographic (PPG) signals as pulse waves. In this study, we designed a PPG recording circuit that was composed of a 600 × 600 µm2 photodiode (PD), an LED driver with pulse wave modulation (PWM) and a low-frequency ring oscillator (RING), and a PPG signal readout circuit. The proposed circuit had a very small area of 2.2 × 1.1 mm2 designed with 0.18 µm CMOS technology. The proposed circuit was used to detect pulse waves on the human fingernail in both the reflection and transmission modes. Electrical characteristics of the prototype system were evaluated precisely and PPG waveforms were obtained successfully.

https://iopscience.iop.org/article/10.7567/JJAP.57.04FM11/pdf

Development of integrated photoplethysmographic recording circuit for trans-nail pulse-wave monitoring system

To restore visual sensation of blind patients suffering from age-related macular degeneration (AMD) and retinitis pigmentosa (RP), we have been developing fully-implantable retinal prosthesis consisting of three dimensional (3-D) stacked retinal prosthesis chip with high density through silicon vias (TSVs), flexible cable, and a stimulus electrode array. Using 3-D integration technology, a photoreceptor chip with more than 1000 pixels can be fabricated in the top layer, and stimulus current generator with various image processing functions can also be fabricated in the bottom layer. In this paper, we presented experimental evaluation results of the stimulus current generator with Laplacian edge-enhancement function. The proposed edge enhancement (EE) function used a four-neighbor Laplacian filter circuit as analog signal processing and was implemented in a 0.18-μm 1P6M CMOS technology. A pixel size including the four-neighbor Laplacian filter circuit was 75 × 75 μm2, and 37 × 37 pixels occupied a very small active circuit area of 3.2 × 3.2 mm2. Experimental results showed the fabricated stimulus current generator completely captured an input image and successfully performed the EE processing for the input image data. Furthermore, total output current from photo-diodes, which became input currents of biphasic pulse generator, was reduced by 87% with the EE circuit. Safer electrical stimulations to the retina cells can be realized with the stimulus current generator with Laplacian EE in the 3-D stacked retinal prosthesis chip.

Experimental evaluation of stimulus current generator with Laplacian edge-enhancement for 3-D stacked retinal prosthesis chip

This paper presents area efficient and ultrawide range square wave impedance analysis circuit for biomedical applications. By using a gate-induced drain-leakage current (GIDL), we designed an ultralow current generation circuit which is a key component of the impedance measurement circuit and a GIDL-controlled oscillator operating at ultralow frequency. In addition, the area of the impedance measurement circuit becomes remarkably small due to square waveform current. All impedance measurement circuits are fabricated with a 0.18μm 1P6M standard CMOS technology and occupy 0.43mm2. As results, the proposed GIDL-controlled oscillator circuit successfully oscillated at ultralow frequency of 3.1Hz, and the impedance measurement circuit completely outputs square waveforms with a current amplitude of 50pA. The proposed circuit can measure impedance ranges from 100Ω to 100MΩ.

Yoshiki Takezawa

Papers

Development of integrated photoplethysmographic recording circuit for trans-nail pulse-wave monitoring system

Experimental evaluation of stimulus current generator with Laplacian edge-enhancement for 3-D stacked retinal prosthesis chip

Ultrawide range square wave impedance analysis circuit with ultra-slow ring-oscillator using gate-induced drain-leakage current

Design and Evaluation of EIT Measurement System with Square Wave Current Source

Evaluation of Stimulus Current Generator with Laplacian Edge-Enhancement for 3-D Stacked Retinal Prosthesis Chip