A single-chip fingerprint sensor and identifier

A chip architecture that integrates a fingerprint sensor and an identifier in a single chip is proposed. The fingerprint identifier is formed by an array of pixels, and each pixel contains a sensing element and a processing element. The sensing element senses capacitances formed by a finger surface to capture a fingerprint image. An identification is performed by the pixel-parallel processing of the pixels. The sensing element is built above the processing element in each pixel. The chip architecture realizes a wide-area sensor without a large increase of chip size and ensures high sensor sensitivity while maintaining a high image density. The sensing element is covered with a hard film to prevent physical and chemical degradation and surrounded by a ground wall to shield it. The wall is also exposed on the chip surface to protect against damage by electrostatic discharges from the finger contacting the chip. A 15×15 mm² single-chip fingerprint sensor/identifier LSI was fabricated using 0.5-μm standard CMOS with the sensor process. The sensor area is 10.1×13.5 mm². The sensing and identification time is 102 ms with power consumption of 8.8 mW at 3.3 V. Five hundred tests confirmed a stranger-rejection rate of the chip of more than 99% and a user-rejection rate of less than 1%     

A pixel-level automatic calibration circuit scheme for capacitive fingerprint sensor LSIs

We propose a pixel-level automatic calibration circuit scheme that initializes a capacitive fingerprint sensor LSI to eliminate the influence of the surface condition, which is degraded by dirt during long-time use. The scheme consists of an automatic calibration circuit for each pixel and a calibration control circuit for the pixel array. The calibration is executed by adjusting variable capacitance in each pixel to make the sensor signals of all pixels the same. The calibration control circuit selects the pixels in parallel, and calibrates all pixels in a short time. The scheme was applied to a fingerprint sensor LSI using the 0.5-/spl mu/m CMOS process/sensor process, and clear fingerprint images were obtained even for a degraded surface condition. This confirms that the scheme is effective for capturing consistent clear images during long-time use.     

A novel sensor cell architecture and sensing circuit scheme forcapacitive fingerprint sensors

Novel capacitive fingerprint sensor techniques are described. We propose a novel sensor cell architecture to obtain high sensitivity, wide output dynamic range, and contrast adjustment. For the architecture, three circuit techniques were developed. A sensing circuit with a differential charge-transfer amplifier enhances sensitivity while it suppresses the influence of the parasitic capacitance of the sensor plate. A wide output dynamic range, which is needed for high-resolution analog-to-digital (A/D) conversion, is achieved by transforming the sensed voltage to a time-variant signal. Finally, the sensing circuit includes an automatic contrast enhancement scheme that uses a variable-threshold Schmitt trigger circuit to distinguish the ridges and valleys of a fingerprint well. The characteristics of a test chip using the 0.5-μm CMOS process show a high sensitivity to less than 80 fF as the detected signal, while the variation of the output signal is suppressed to less than 3% at ±20% variation of the parasitic capacitance. The dynamic range of the time-variant signal is 70 μs, which is wide enough for A/D conversion. The automatic contrast enhancement scheme widens the time-variant signal 100 μs more. A single-chip fingerprint sensor/identifier LSI using the proposed sensing circuit scheme confirms the scheme's effectiveness     

A low-noise low-offset capacitive sensing amplifier for a 50-/spl mu/g//spl radic/Hz monolithic CMOS MEMS accelerometer

This paper describes a CMOS capacitive sensing amplifier for a monolithic MEMS accelerometer fabricated by post-CMOS surface micromachining. This chopper stabilized amplifier employs capacitance matching with optimal transistor sizing to minimize sensor noise floor. Offsets due to sensor and circuit are reduced by ac offset calibration and dc offset cancellation based on a differential difference amplifier (DDA). Low-duty-cycle periodic reset is used to establish robust dc bias at the sensing electrodes with low noise. This work shows that continuous-time voltage sensing can achieve lower noise than switched-capacitor charge integration for sensing ultra-small capacitance changes. A prototype accelerometer integrated with this circuit achieves 50-/spl mu/g//spl radic/Hz acceleration noise floor and 0.02-aF//spl radic/Hz capacitance noise floor while chopped at 1 MHz.     

A capacitive fingerprint sensor chip using low-temperature poly-Si TFTs on a glass substrate and a novel and unique sensing method

We have developed a capacitive fingerprint sensor chip using low-temperature poly-Si thin film transistors (TFTs). We have obtained good fingerprint images which have sufficient contrast for fingerprint certification. The sensor chip comprises sensor circuits, drive circuits, and a signal processing circuit. The new sensor cell employs only one transistor and one sensor plate within one cell. There is no leakage current to other cells by using a new and unique sensing method. The output of this sensor chip is an analog wave and the designed maximum output level is almost equal to the TFT's threshold voltage, which is 2-3 V for low-temperature poly-Si TFTs. We used a glass substrate and only two metal layers to lower the cost. The size of the trial chip is 30 mm/spl times/20 mm/spl times/1.2 mm and the sensor area is 19.2 mm/spl times/15 mm. The size of the prototype cell is now 60 /spl mu/m/spl times/60 /spl mu/m at 423 dpi, but it will be easy to increase the resolution up to more than 500 dpi. The drive frequency is now 500 kHz and the power consumption is 1.2 mW with a 5-V supply voltage. This new fingerprint sensor is most suitable for mobile use because the sensor chip is low cost and in a thin package with low power consumption.     

Reset noise reduction in capacitive sensors

Reset noise sets a fundamental detection limit on capacitive sensors. Many sensing circuits depend on accumulating charge on a capacitor as the sensing method. Reset noise is the noise that occurs when the capacitor is reset prior to the charge accumulation cycle. Therefore, it is important to understand the factors which determine reset noise, and how this noise may be mitigated. The purpose of this paper is to show how capacitive reset noise can be reduced during the reset cycle. We present and analyze three circuits that implement the basic methods for directly reducing capacitive reset noise. In addition, we present a time-domain technique for analyzing the time-varying statistics of these circuits. This technique makes use of Ito/spl circ/ calculus to obtain solutions to the time-varying stochastic differential equations. Theoretical noise calculations and Monte Carlo simulation results are presented for each technique. We show that theory and simulation yield similar results. Finally, we show in the examples that reset noise may be reduced by a factor of 20 or more. We also refer to implemented sensor arrays which achieve these results.     

Study of Capacitive Tilt Sensor with Metallic Ball

In this paper, a new, simple capacitive tilt sensor with a metallic ball is proposed. The proposed tilt sensor has only two electrodes and a metallic ball, and this design assists in managing the inherent contact problem in measuring tilt angles. Capacitive sensing, compared with other types of tilt sensor, has many advantages such as simplicity, noncontact measurement, long‐throw linear displacement, and sub‐micron plate spacing. Its design and fabrication process are significantly simpler than previous types of tilt sensors. The dimensions of the prototype tilt sensor are , and the diameter of the polystyrene tube is 5 mm with a tube thickness of 0.15 mm. An analytical study of the prototype capacitive tilt sensor was undertaken, and the experimental results demonstrate the relationship between the tilt angles and measured capacitances compared with the analytical study.     

A capacitive tactile sensor array for surface texture discrimination

This paper presents a silicon MEMS based capacitive sensing array, which has the ability to resolve forces in the sub mN range, provides directional response to applied loading and has the ability to differentiate between surface textures. Texture recognition is achieved by scanning surfaces over the sensing array and assessing the frequency spectrum of the sensor outputs.     

Low-voltage lab-on-chip for micro and nanoparticles manipulation and detection: experimental results

In this paper, a low voltage fully integrated Laboratory-on-Chip (LoC) for dielectrophoretic manipulation and capacitive sensing of nano and micro particles is presented. The proposed system is intended to design an implantable LoC. The lowest static power consumption of the implemented Integrated circuit is 650???A with a voltage supply of ?1.10 and +1.8?V. Three different sizes of carboxyl-modified polystyrene particles (diameters of 0.22, 0.97 and 2.04???m) where tested experimentally with three different electrode architectures to achieve dielectrophoretic mixing and separation. U-shaped, L-shaped and octagonal electrodes are used to perform the separation and mixing operations. The biosensing part is designed with a charge based capacitive sensor with an integrated sigma-delta modulator at its output stage. It was tested experimentally with algae and ethanol. The chip size is 1.2 by 1.2?mm and it is connected to a 15?×?30?cm microfluidic design. An efficient particle manipulation was achieved by applying a voltage of 1.7 V peak to peak in the microchannel with 90 and 180° dephased signals.     

USB型指纹采集仪的设计与实现

介绍了一种新型CMOS指纹传感芯片--FPS200的性能、结构及工作原理,实现了基于FPS200芯片的USB型指纹采集仪的设计,并对设计中要注意的问题进行了具体说明.该采集仪具有自动检测指纹、上传图像快、结构简单和使用方便等特点.     

Inkjet and microcontact printing of functional materials on foil for the fabrication of pixel-like capacitive vapor microsensors

The work presented demonstrates the utilization of micro-contact printing of self-assembled monolayers (SAMs) of gold nanoparticles (NPs) to pattern the porous thin metallic film composing the top electrode of an ultra-fast capacitive relative humidity sensor based on miniaturized parallel-plates electrodes. The rest of the device, which occupies an area of only 0.0314 mm², is fabricated by inkjet printing stacked individual drops of functional materials, namely gold NPs for the bottom electrode and a polymeric humidity sensing layer, on a polymeric foil. Compared to other printing methods, the use of microcontact printing to pattern the top electrode enables the additive transfer of a solvent-free metallic layer that does not interact chemically with the sensing layer, permitting the thinning of the latter without risk of short-circuits between electrodes, and broadening the range of usable sensing materials for detection of other gases. Thinning the sensing layer yields to ultra-fast response devices with high values of capacitance and sensitivity per surface area. The fabrication process is compatible with low heat-resistant polymeric substrates and scalable to large-area and large-scale fabrication, foreseeing the development of low-cost vapor sensing sheets with high space–time resolution, where every sensor would correspond to a pixel of a large array.     

A CMOS-only micro touch pointer

A direct-contact finger mouse realized in 0.7-μm digital CMOS is presented. It is based on the motion detection of the fingerprint images acquired with a capacitive sensor. Stroking and tapping the chip surface with the finger causes movement of the cursor and clicking-like mouse. By properly partitioning analog collective computation and digital processing, a power consumption of about 900 μW at 5 V is achieved. The sensor area is 3.8×3.8 mm², and overall chip size is 7.7×6.7 mm²     

A 600-dpi capacitive fingerprint sensor chip and image-synthesistechnique

This paper examines the possibility of a low-cost, high-resolution fingerprint sensor chip. The test chip is composed of 64×256 sensing cells (chip size: 2.7×10.8 mm²). A new detection circuit of charge sharing is proposed, which eliminates the influences of internal parasitic capacitances. Thus, the reduced sensing-capacitor size enables a high resolution of 600 dpi, even using a conventional 0.6 μm CMOS process. The partial fingerprint images captured are synthesized into a full fingerprint image with an image-synthesis algorithm. The problems and possibilities of this image-synthesis technique are also analyzed and discussed     

基于嵌入式处理器指纹识别系统的设计和实现

研究采用嵌入式处理器实现指纹识别系统的软硬件设计方法．通过构造以微处理器AT91SAM7X256和MBF200指纹传感器模块为平台的硬件环境,实现了嵌入式指纹识别硬件系统的设计。微处理器选用内含丰富外设的AT91SAM7X256,降低了硬件成本。指纹识别系统选用μC／OS-Ⅱ作为嵌入式操作系统,指纹识别算法中主要介绍了基于图像匹配的指纹识别算法、基于Gabor函数的指纹图像增强算法和基于方向图滤波指纹特征提取算法等．实现了低成本,高可靠性多节点指纹识别系统的设计。     

低迟滞MEMS电容式气压传感器设计

针对传感器的机械迟滞问题,提出一种减小迟滞偏移的方法,设计了低迟滞误差的电容式气压传感器。使用ANSYS和FLUENT软件模拟电容式传感器的工作性能,分析传感器的温漂特性、电容灵敏度及加热功率与通孔大小的匹配问题。分析结果表明传感器的电容温漂为0.029 fF/K,电容灵敏度为30 fF/hPa;加热空腔气体可以驱动空腔内气压增加20 hPa,超过传感器的迟滞误差范围,为低迟滞误差传感器的设计和结构优化提供了依据。     

Exploration on Solvatochromic Sensing Probe of Phenol Blue for L-Lactic Acid Detection: Effective Strategy to Obtain Reliable Capacitive Sensor

This study systematically investigates a capacitive sensor applied with phenol blue (PhB)-based sensing medium for detection of L-lactic acid (LA), as a health monitoring indicator. PhB is a substance with solvatochromic effect, inducing the change in capacitance by exposure to polar molecules. However, the capacitive LA sensor with a flat-structured PhB/polyvinylchloride (PVC) composite-sensing medium is observed to have a problem in that sensing capacitance variation saturate quickly with increasing the LA solution concentration. This main cause can be analyzed that the interaction of proton from LA molecule with the lone pair electrons of the PhB molecule acts as a major factor on the sensing characteristics rather than the solvatochromic behavior of PhB molecule. Therefore, a strategy is adopted to introduce a porous structure to the PhB/PVC composite-sensing medium to maximize the interaction of PhB with protons, which is implemented through solvent and non-solvent exchange methods. Consequently, the sensitivity and linearity of the porous-structured LA sensor are 2.99 pF mm ⁻¹ and 0.966 over LA concentrations ranging from 0 to 100 mm , respectively, which is a significant improvement over that of the flat-structured one. Notably, the sensing performance remained unchanged even after a month of storage under normal ambient conditions.     

新型磁驱动增大检测电容的高精度MEMS惯性传感器研究

增大传感器振子的质量和静态测试电容可以减小电容式MEMS惯性传感系统的噪声,而深度粒子反应刻蚀工艺由于复杂的工艺原因,当深宽比较大时,不能刻蚀出大质量和大初始电容的传感器.据此,本文研究了一种磁驱动增大检测电容的MEMS惯性传感器,通过电磁驱动器,传感器的静态测试电容可以大幅增加,在梳齿电容上刻蚀阻尼槽后,其机械噪声达到0.61μg每根号赫兹,仿真其共振频率为598Hz,静态位移灵敏度为0.7μm每重力加速度,基于硅 玻璃键合工艺,制作了栅形条电容式惯性传感器,并用电磁驱动的方式测试其品质因子达到715,从而验证了制作工艺的可行性和电磁驱动器改变传感器初始静态测试电容的可行性.     

Cobalt oxide nanosheet humidity sensor integrated with circuit on chip

The work studies a micro humidity sensor integrated with a seven-stage ring oscillator circuit-on-a-chip fabricated by the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process and a post-process. The structure of the humidity sensor consists of interdigitated electrodes and a sensing film. The sensing film is cobalt oxide nanosheet that is prepared by a precipitation-oxidation method. The sensor, which is a capacitive type, changes in capacitance when the sensing film adsorbs or desorbs water vapor. The ring oscillator circuit is employed to convert the capacitance of the sensor into the oscillation frequency output. The post-process of the sensor includes etching the sacrificial oxide layer and coating the sensing film on the interdigitated electrodes.     

基于LPC2368的嵌入式多节点指纹识别系统设计

以集成以太网控制器和CAN总线控制器的ARM7处理器LPC2368为核心,MBF200芯片为指纹传感器模块,PCA82C250为CAN总线收发器芯片,重点阐述了系统接口部分硬件电路图设计和系统软件构建。实现了低成本,高可靠性多节点指纹识别系统的设计。     

基于DSP的指纹自动连续采集系统

指纹自动连续采集系统是以DSPTMS320VC5402为核心,与MBF200型指纹传感器相结合,并通过USB接口与主机实现通信,采用VB将定时自动采集到的指纹在采集界面显示,然后选择效果最好的指纹,并存储到相应数据库中。该系统采集的指纹识别率高,具有很强的实用价值。