具翹板致動結構之全像光學感測器研究應用於微型化光儲存裝置

Abstract

光資訊儲存經過數十年的發展後，已經達到了高數值孔徑的藍光儲存系統，一般認為這是傳統碟片型光儲存方式繞射極限最為有效的發揮，屆時需要新的儲存技術來將儲存密度推向極致，達到單一碟片即有兆位元的儲存容量的需求，而未來的技術則可能是近場儲存或全像式儲存等不同的系統架構，除了技術領域的研究外，重要的研究目標則是儲存系統應用與開發。在各式應用中，重點研發項目就是各式可攜式微型儲存系統：光儲存微型光碟、磁儲存微型硬碟、以及快閃記憶體等各式可攜式多媒體播放電子產品。目前的市場而言，仍以微型硬碟和快閃記憶體為主要可自主讀寫產品，因此，本研究針對微型光碟系統所開發微型光學讀取頭元件、模組及致動器雛型，進一步以系統的角度加以整合，對日後高儲存密度技術之需求進行光學系統技術之研發，以實際產品開發所需符合的特性參數為依據，發展微型光學讀取頭裝配技術，以供可攜式光儲存裝置使用，進一步整合搭載雙軸向微致動器進行訊號讀取與控制，為次世代光儲存產業奠定基礎。微型光學頭以全像光學元件替代傳統分光鏡及圓柱透鏡來產生聚焦與循軌伺服訊號，本研究先以模組及系統整合為重點，在微型光學讀取頭製造過程中，發展以覆晶封裝機台為主軸的晶圓級微光學系統組裝技術，將微機電系統概念導入組裝過程中，以期大幅減少傳統組裝過程中的困難及成本。過程中並將開發此對位與組裝技術所需驗證機台或夾持機構設計，利用覆晶封裝機台中的對準功能，將微型光學元件黏著於矽光學載台上堆疊成完整的微光學系統架構，以光學設計軟體分析微光學系統其元件製作與系統組裝公差再進行優化，取得光學頭聚焦與循軌過程中光碟片上聚焦光點分佈，為驗證此微光學讀取頭性能並保持雷射光束不被破壞且有高品質聚焦光點。組裝流程須針對微光學組件進行光學與電性品質量測與驗證，另一方面光學頭組裝品須架設於可做聚焦及循軌之致動器機構上，以能隨碟片旋轉而讀取碟片位元資料，本研究所搭載微型化光學頭之翹板式微懸臂雙軸向致動器概念乃有別於傳統四軸式與懸臂式光學致動器的創新機構，所進行致動器結構形狀優化與驅動音圈馬達磁路最佳化分析使相關規格符合光學系統動態需求，進一步改善翹板式聚焦驅動時光軸傾角所產生光學品質劣化，採取懸臂前端內嵌壓電片進行光軸補償雙軸驅動機制，以聚焦音圈馬達為主致動器搭配壓電片微致動器修正光軸傾角，雙軸聚焦驅動修正徑向光軸偏移與提升光學品質，提供次世代微型化光儲存系統良好的精密機構定位平台載具。

An optical head composed of an optical module and a biaxial seesaw swivel actuator is designed for small form factor drives. This optical configuration has been fabricated and assembled for the proposed 635nm red-light small form factor (SFF) optical pickup head system. This system adopts a finite-conjugate objective lens with numerical aperture (NA) 0.65 for 635nm wavelength. A holographic optical element (HOE) is used for simplifying the optical configuration which provides a better approach for passive alignment. The assembly and alignment of various micro-optical components in optical pickup unit assembly were facilitated by using a flip chip bonder. Technological obstacles to the use of rotary-type swing arm actuators to actuate optical pickup modules in SFF disk drives stem from a hinge’s skewed actuation, subsequently inducing off-axis aberrations and deteriorating optical quality. Many SFF optical pickup heads based on the swing arm design utilize piezoelectricity or slim plate of metal to perform focusing action. The dual-stage seesaw type actuator is an enhanced driving mechanism used for swiveling the entire optical pickup heads devices. The configuration of the seesaw swivel actuator has unique features including a rotary actuator for coarse and fine tracking and a seesaw arm for swiveling along a pivot instead of a hinge to permit a tilt focus movement. A triple-layered bimorph bender made of piezoelectric materials (PZTs) is connected to the suspension of the pickup head, while the tunable vibration absorber unit is mounted on the seesaw swing arm to offer a balanced force to reduce vibrations in a focusing direction. The PZT micro-actuator is designed to satisfy stable focusing operation operational requirements and compensate for the tilt angle variation in focusing stroke. The performance of the biaxial dual-stage actuator is verified through simulation by finite-element methods, and the effectiveness is confirmed by experimental procedures and parametric design optimization. This integrated optical disk drive device, SFF optical module and dual-stage seesaw swivel actuator, is effectively self-aligned the optical axis for read/write performance in both experiment and simulation result. Dynamic measurements of motion trajectory based on laser sensing reveal significant optical axis correction with and without PZT micro-actuator compensation. The fabrication methodology for a dual-stage seesaw swivel actuator with SFF optical pickup module is investigated. Furthermore, the performances of dual-stage leverage mechanism based on optical sensing are experimentally evaluated to demonstrate the effectiveness of active tilt compensation. Simulation and experimental results are satisfactory and provide the feasibility of realizing the high-density portable optical storage system in compactness.