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PCBD-June2017

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44 The PCB Design Magazine • June 2017 nents, gradual strengthening of functions and gradual densification of signal transmissions call for participation of more low-capacitance bypass capacitors to eliminate electromagnetic coupling and signal crosstalk. Therefore, em- bedded capacitor PCB technology has attracted a wide range of attention by the industry. Merits of Embedded Resistors Advantages of embedded resistors mainly come in three aspects: electrical performance, PCB design and reliability. Electrical Advantages • Helps improve line impedance matching • Leads to shorter signal paths and decreased series inductance • Causes reduction of cross talk, noise and EMI PCB Design Advantages • Leads to active component density improvement and decreased form factors • Calls for no requirement of vias, leading routing to improvement • Results in simplified boards, shrinking size and/or densification Improved Reliability It benefits from its improved reliability, which can be summarized into Table 1. Factors Determining Performance of Thin Film Up to now, thin-film resistor material cov- ers a wide application range containing chro- mium material, tantalum material and tita- nium material. Compared with chromium thin-film resistors, tantalum thin-film resistors feature many excellent performances such as excellent chemical stability and corrosion re- sistance, high reliability, wide resistance range and high stability, which makes it an ideal thin-film resistor material with a broad appli- cation prospect. Uniformity of resistor thin film refers to the situation in which how resistors fabricated on the substrate change as substrate position changes in vacuum cavity and how resistance modifies as the same substrate moves. The lead- ing factors driving uniformity of thin film in- clude: relative position between substrate and target material, deposition rate and vacuum de- gree. Tantalum nitride (TaN) film applicable to thin-film ICs features excellent uniformity both on the same substrate and between substrates from different positions. Moreover, resistance errors between different batches remain low with excellent uniformity. Currently, two preparation methods are available for TaN film preparation: physical va- por deposition and chemical vapor deposition. Stability and reliability, accuracy and uniformity of electrical resistivity play an important role in TaN film manufacturing. Up to now, resistance is modified mainly through laser or oxidation to ensure the accuracy of resistance. Both meth- ods, however, feature some drawbacks that laser possibly damages resistance graphics with pow- er withstand by resistor film whereas resistance modification through oxidation suffers from a low rate and bad reliability. This article takes advantage of magnetron reactive sputtering to prepare TaN thin film and studies the influence of technical parameters such as uniform plate position on TaN thin-film uniformity and performance, determining ac- curate controlled technology of resistance rate. Furthermore, it studies and analyzes deposition scanning rate and effects of flow ratio of N 2 on TaN thin film and performance. Performance Analysis of Thin Film Uniformity Analysis Under the condition of fixed scanning speed of 105cm/min and 10% of nitrogen flow ratio, uniformity is analyzed for TaN thin film. Inner sheet uniformity can be figured out through the following formula: Table 1: Determining performance of thin film. PERFORMANCE EVALUATION OF THIN-FILM EMBEDDED RESISTORS

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