室溫紅外線偵檢器與圓形極化天線在無線微感測器應用上的設計,製作與模擬分析

Abstract

一個無線微感測器主要可以分為三個部分：天線、積體電路以及感測器。一般而言,由於積體電路以及感測器所占面積相對於天線尺寸顯得相當的微小，因此，一個無線微感測器所佔有的面積主要由天線的大小來做決定。此外，對於一個無線微感測系統而言，系統的功率損耗以及系統的傳輸距離在設計時都必須加以考慮進去。本論文主要針對如何製作用來感測物體溫度的室溫紅外線偵檢器以及如何製作一個可與積體電路與感測器整合的圓形極化天線，此外對於無線微感測器的傳輸距離以及射頻訊號的轉換特性都做了一些評估。因此本論文主要分成三個部分:第一部分為”無線微感測系統的效能評估”;第二部分為”低溫CMOS製程相容之室溫紅線感測器的設計與模擬分析”;第三部分為”適用於無線微感測器之圓形極化槽孔天線設計與模擬分析”。 在第一部分中，為了降低系統的功率損耗以及有效利用接收到的電磁波能量，我們利用無線射頻辨識技術(RFID)來製作一個零偏壓的天線整流器(rectenna)，此天線整流器的輸出受到訊號傳輸距離的影響，為了精確評估電磁波能量的接收以及高頻訊號的轉換，因此我們利用高頻3D電磁場軟體以及高頻電路軟體來模擬收發系統間的訊號傳輸特性。 在第二部分中，我們為了使積體電路與微感測器之間的訊號損耗降低以及增加感測訊號的靈敏度，我們採用在積體電路製作完成後於其上實現我們的紅外線微感測器。爲了達到此一目標，我們必須將整個元件陣列的製程溫度限制在低於400 oC，同時配合面型微細加工技術以及 CMOS製程相容的方法來縮小每個紅外線感測陣列的像素面積以及降低元件的製作成本，進而提高系統的解析度以及增加陣列元件的積集度。在元件材料選擇上，我們採用二氧化矽當作元件的結構層、鋁當犧牲層、摻雜的非晶矽當作感測材料層、鉭用來當做金屬訊號傳導層，同時利用另一薄鋁層當作反射層來製作四分之一波長共振腔增加紅外線的吸收率，此元件的材料選擇可以達到幾乎百分之百的蝕刻選擇比，對於元件的製程上是相當穩定。此外，在元件最後乾燥過程中，我們也探討如何利用現有簡單的熱板設備取代目前常用的昂貴二氧化碳超臨界點來達到元件的高良率以及高可靠度，以利元件的進一步大量製造。對於元件的結構分析，我們使用CoventorWare軟體，在元件犧牲層釋放過程中，用來預測整個元件的浮板結構變形狀況，進一步用來判斷浮板懸浮與否。對於元件的熱分析，我們使用Ansys有限元素分析軟體來計算元件的溫度分布、熱時間常數以及熱流通量。 就天線而言，目前大部分的無線微感測器大都利用線性極化天線來傳輸感測訊號，線性極化天線往往因為傳輸端與接受端的天線角度誤差，而造成傳輸系統的極化損耗，最大損耗可達30dB，然而對於圓形極化系統而言則可以避免此一損耗產生。圓形極化天線在設計上比線性極化天線困難很多，加上目前尚未有縮小化圓形極化天線出現過，因此對於圓形極化天線研究的人更少。目前大部分圓形極化天線主要以微帶天線居多，主要是因為微帶天線在設計上槽孔天線容易，然而槽孔天線卻有比微帶天線更寬的阻抗頻寬、圓形極化頻寬。在第三部分中，我們在目前常用的商業基板FR4(介電常數4.4，厚度1.6 mm，基板損耗正切0.0245)上創新設計出許多不同類型的圓形極化行波槽孔天線，有別於傳統的圓形極化共振型槽孔天線。這些圓形極化行波槽孔天線操作於2.4 GHz ~2.5 GHz頻段範圍，S參數都低於 -30 dB，天線輻射增益都在3 dBi以上，天線輻射效率大於85%，以及3 dB圓形極化軸比在空間分部至少涵蓋正負30度以上的俯角，而饋入的方式有微帶線訊號饋入以及共平面波導訊號饋入兩種，天線輸入阻抗匹配到射頻系統的50歐姆。我們藉由電磁模擬軟體Zeland IE3D來進行2.5D的天線設計與模擬分析，接著利用Ansoft HFSS來觀察天線3D結構的電磁分佈，這是因為IE3D對於開發平板天線的時效上有其優勢，而HFSS對於空間中的電磁分佈有其獨到之處。天線阻抗量測部分使用網路分析儀，而輻射場形部分使用HP85301C於無反射波量測實驗室進行。

A wireless microsensor can be divided into three main parts: Antenna, integrated circuit (IC), and micro-sensor. Generally, the total area of IC and micro-sensor is very little as compared with the antenna area, and therefore the area of a wireless microsensor is dependent on the antenna area. Besides, for a wireless microsensing system, the power loss of a system and the transmission distance must be taken into account during the system design. The purpose of this dissertation focus on how to fabricate the uncooled infrared detector array using to sense the infrared from objects and how to develop the circularly polarized slot antenna using to integrate with IC and micro-sensor. Besides, we also evaluate the transmission distance and the RF signal conversion characteristics of the wireless microsensing system. Consequently, this dissertation includes three parts: Part I “Performance evaluation of wireless microsensing system”; Part II “Design and simulation of an uncooled microbolometer with low temperature CMOS-process compatibility”, Part III “Design and simulation of circularly polarized slot antennas for wireless micro-sensor applications”. In Part I, in order to decrease the system power loss and increase efficiently the use of the received electromagnetic power, we use the radio frequency identification technology (RFID) to design a zero-bias rectenna (antenna and rectifier). The output of the rectenna is affected by the signal transmission distance. In order to exactly estimate the received EM power and RF signal conversion, we use a 3-D high frequency EM software and a high frequency circuit software to simulate the signal transmission characteristics between the transmitter and the receiver. In Part II, in order to reduce the signal loss and increase the sensing signal sensitivity between IC and micro-sensor, we implement our infrared micro-sensor directly fabricated on the top of IC. Achieving the preceding purpose, the whole processing temperature must be limited to below 400 degrees. At the same time, the surface micromachining technology and CMOS-process compatible method used to reduce the pixel size of infrared sensor array and lower the device-processing cost can further improve the system resolution and increase the device fill factor. With respect to material selection, we use silicon dioxide as the structural layer, Al as sacrificial layer, doped amorphous silicon as the sensitive layer, and Ta as the signal conducting line. Besides, we also use aluminum as a mirror layer to develop a quarter-wavelength resonator to increase infrared absorption. These materials providing nearly 100% etching selectivity is very stable during device fabrication. In addition, we also discuss how to use simple and cheap hot plate instead of expensive apparatus of CO2 supercritical to achieve high yield and high reliability during device drying step. This is a great benefit to mass production. Considering device structural analysis, we use CoventorWare simulator to predict the status of the device structure deformation to further determine whether the membrane is suspend or collapsed during device releasing step. With respect to thermal simulation, Ansys which is a FEM simulator is used to estimate the temperature distribution, thermal time constant, and heat flux distribution of the device. In terms of antenna, nowadays the most use of antenna communicating signal for wireless micro-sensor is the linearly polarized antenna. However, the polarization misalignment between the antennas of the transmitter and receiver always results in polarization loss, the maximum loss being 30dB possible. But with respect to circularly polarized (CP) system, the polarization loss can be alleviated. Only a few of the studies related to circularly polarized antenna are done due to the difficulty of the CP antenna. In addition, the compact size of CP antenna is never presented. Because the CP microstrip antennas are easier design than the CP slot antennas, the most of CP antennas are microstrip antenna. However, the slot antenna has wider impedance bandwidth, axial-ratio bandwidth over the microstrip antenna. In Part III, we develop several novel design CP traveling wave slot antennas on the common use substrate of FR4 (dielectric constant of 4.4, height of 1.6 mm, and loss tangent of 0.0245), and these proposed slot antennas are different from other traditional CP resonator slot antenna. These proposed slot antennas have several characteristics such as the operating frequency of 2.4 ~2.5 GHz, the S parameter of lower than -30 dB, the antenna gain above 3 dBi, the antenna radiation efficiency of above 85 %, and the 3 dB Axial-ratio at least cover the 30 degrees at the elevation direction. The feed types of the proposed antennas include microstrip feed and coplanar waveguide (CPW) feed. The Antenna input impedance also matches to 50 Ohm of the general RF system. We use electromagnetic simulator of Zeland IE3D to design and simulate the 2.5D antenna structure followed by using Ansoft HFSS to observe the 3D electromagnetic distribution. This is because the IE3D is superior to HFSS in analyzing time. However, the HFSS can exactly display the 3D electromagnetic distribution in the free space. The antenna impedance is measured by network analyzer, and the radiation pattern is measured by HP 85301C in the non-reflection chamber.