500 research outputs found
Determination of bulk discharge current in the dielectric film of MEMS capacitive switches
The present work presents a new method to calculate the discharge current in the bulk of dielectric films of MEMS capacitive switches. This method takes into account the real MEMS switch with non uniform trapped charge and air gap distributions. Assessment of switches with silicon nitride dielectric film shows that the discharge current transient seems to obey the stretched exponential law. The decay characteristics depend on the polarization field’s polarity, a fact comes along with experimental results obtained from thermally stimulated depolarization currents (TSDC) method used in MIM capacitors
Charge Collection Mechanism in MEMS Capacitive Switches
The present paper investigates the effect of stressing bias magnitude and stressing time on the discharging process in MEMS capacitive switches. The calculation of discharge current through the dielectric film is based on monitoring the rate of shift of bias for up-state minimum capacitance. The data analysis shows that the discharge current lies in the range of femto-Amperes and the calculated discharge time constant depends directly on the time window of observation and on the stressing conditions. Moreover the analysis reveals an increase of trapped charge that remains in the bulk of the dielectric film for very long time as the stressing bias increases. The dominant discharge process, taking place under an intrinsic field of about 10^3 V/cm, is found to be the hopping effect
Charging and Discharging Processes in AlN Dielectric Films Deposited by Plasma Assisted Molecular Beam Epitaxy
In the present work the electrical properties of AlN polycrystalline films deposited at low temperatures by plasma-assisted molecular beam epitaxy (PA-MBE) are investigated. The polarization build-up during constant current injection as well as the depolarization process after the current stress have been investigated through monitoring voltage transients in Metal – Insulator – Metal (MIM) capacitors, in temperature range from 300 K to 400 K. Moreover, current – voltage characteristics obtained at different temperatures revealed that charge collection at low fields in these films occurs through variable range hopping
A MIM CAPACITOR STUDY OF DIELECTRIC CHARGING FOR RF MEMS CAPACITIVE SWITCHES
MIM capacitors are considered equally important devices for the assessment of dielectric charging in RF MEMS capacitive switches.Beside the obvious similarities between the down state condition of RF MEMS and MIM capacitors there are also some important differences. The paper aims to introduce a novel approach on the study of dielectric charging in MEMS with the aid of MIM capacitors by combining experimental results obtained by the application of DC, Charging Transient and Kelvin Probe techniques.The strengths and weaknesses are discussed in conjuction with experimental results obtained on SiNx based MIM capacitors ans MEMS capacitive switches fabricated under the same conditions
Μελέτη και Βελτιστοποίηση των Ηλεκτρικών Ιδιοτήτων Λεπτών Μονωτικών Υμενίων που Χρησιμοποιούνται σε Μικρο-Ηλεκτρο-Μηχανικά Συστήματα (MEMS)
Οι διακόπτες RF MEMS αποτελούν ιδιαίτερα υποσχόμενες διατάξεις στον τομέα των τηλεπικοινωνιών όμως προβλήματα αξιοπιστίας εμποδίζουν την εμπορευματοποίησή τους έως και σήμερα. Η παρούσα διατριβή εξετάζει ένα από τα σημαντικότερα προβλήματα αξιοπιστίας που συναντάται στους διακόπτες αυτούς, τη φόρτιση των διηλεκτρικών τους υμενίων. Τα υμένια των διακοπτών RF MEMS εναποτίθενται με σύγχρονες μεθόδους της μικροηλεκτρονικής και εμφανίζουν σημαντικό βαθμό ανομοιογένειας και απόκλιση από τη στοιχειομετρία. Στόχος της διατριβής είναι η κατανόηση των μηχανισμών πόλωσης και αποπόλωσης των διηλεκτρικών υμενίων καθώς επίσης και η μελέτη της επίδρασης των συνθηκών εναπόθεσης στα ηλεκτρικά τους χαρακτηριστικά. Το διηλεκτρικό υλικό που μελετήθηκε είναι το νιτρίδιο του πυριτίου, οι ηλεκτρικές ιδιότητες του οποίου δεν είναι ακόμη πλήρως γνωστές παρά το γεγονός ότι αποτελεί ένα από τα πιο διαδεδομένα υλικά στην μικροηλεκτρονική
Μελέτη και βελτιστοποίηση των ηλεκτρικών ιδιοτήτων λεπτών μονωτικών υμενίων που χρησιμοποιούνται σε Μικρο-Ηλεκτρο-Μηχανικά Συστήματα (MEMS)
Οι χωρητικοί διακόπτες RF MEMS αποτελούν ιδιαίτερα υποσχόμενες διατάξεις στον
τομέα των τηλεπικοινωνιών όμως προβλήματα αξιοπιστίας εμποδίζουν την
εμπορευματοποίησή τους έως και σήμερα, με σημαντικότερο τη πόλωση των
διηλεκτρικών τους υμενίων. Στόχος της διατριβής είναι η κατανόηση των
μηχανισμών πόλωσης και αποπόλωσης των διηλεκτρικών υμενίων νιτριδίου του
πυριτίου καθώς επίσης και η μελέτη της επίδρασης των συνθηκών εναπόθεσης στα
ηλεκτρικά τους χαρακτηριστικά.
Οι ηλεκτρικές ιδιότητες των υμενίων νιτριδίου του πυριτίου εξετάσθηκαν αρχικά
για διάφορες συνθήκες πόλωσης. Οι διαδικασίες πόλωσης και αποπόλωσης στα
διηλεκτρικά υμένια που μελετήθηκαν βρέθηκε σε κάθε περίπτωση να είναι θερμικά
ενεργοποιούμενες και σύνθετες. Η επίδραση των συνθηκών εναπόθεσης της μεθόδου
PECVD στα ηλεκτρικά χαρακτηριστικά των υμενίων νιτριδίου του πυριτίου
μελετήθηκε στη συνέχεια διεξοδικά. Επιπλέον, προτάθηκε μια νέα πειραματική
μέθοδος που επιτρέπει τον προσδιορισμό του ρεύματος εκφόρτισης λόγω μεταφοράς
των φορτίων διαμέσου των διηλεκτρικών υμενίων. Κυρίαρχος μηχανισμός
αγωγιμότητας κατά την αποπόλωση των μελετώμενων υμενίων βρέθηκε να είναι οι
διαδικασίες hopping. Επίσης, με τη βοήθεια της προτεινόμενης μεθόδου
πραγματοποιήθηκε ξεχωριστή μελέτη των θερμικά ενεργοποιούμενων διαδικασιών
πόλωσης και αποπόλωσης. Η συνεισφορά των επιμέρους μηχανισμών πόλωσης στη
συνολική φόρτιση των υμενίων νιτριδίου του πυριτίου μελετήθηκε τέλος ξεχωριστά
σε διακόπτες RF MEMS, πραγματοποιώντας μετρήσεις πόλωσης εξ επαφής και εξ
επαγωγής των διηλεκτρικών υμενίων.Capacitive RF MEMS switches are one of the most promising devices for RF
applications but reliability problems still hinder their commercialization, the
most important being the effect of dielectric charging. The present thesis aims
to provide a better understanding of charging and discharging processes that
appear in silicon nitride dielectric films used in RF MEMS switches.
First, the electrical characteristics of silicon nitride films have been
investigated for different polarization conditions. The results indicate that
charging and discharging processes are thermally activated and consistent to
Kohlrausch-Williams-Watts polarization’s relaxation, found in many materials
containing some degree of disorder. The effect of deposition conditions of
PECVD method on the electrical properties of silicon nitride films has been
also probed. A new experimental method has been proposed in the present thesis
that allows the determination of discharging current through the bulk of the
dielectric films in RF MEMS switches. The results indicate that the dominant
conduction mechanism during discharge in silicon nitride films are the hopping
processes. Moreover, thermally activated charging and discharging mechanisms
have been investigated separately with the aid of the proposed method mentioned
above. Finally, the contribution of each charging mechanism to the total
polarization of silicon nitride films has been probed by performing contacted
and contact-less charging procedures in RF MEMS switches and it is found that
induced charging mechanisms could act as a compensation mechanism to the total
polarization of dielectric films
Characterisation and modelling of degradation mechanisms in RF MEMS capacitive switches during hold-down operation
RF MEMS switches represent an attractive alternative technology to current mechanical (e.g. coaxial and waveguide) and solid-state (e.g. PIN diode and FET transistor) RF switch technologies. The materials and fabrication techniques used in MEMS manufacture enable mechanically moveable devices with high RF performance to be fabricated on a miniature scale. However, the operation of these devices is affected by several mechanical and electrical reliability concerns which limit device lifetimes and have so far prevented the widespread adoption and commercialisation of RF MEMS. While a significant amount of research and development on RF MEMS reliability has been performed in recent years, the degradation mechanisms responsible for these reliability concerns are still poorly understood. This is due to the multi-physical nature of MEMS switches where multiple mechanical and electrical degradation mechanisms can simultaneously affect device behaviour with no clear way of distinguishing between their individual effects. As such, little progress has been made in proposing solutions to these reliability concerns. While some RF MEMS switches have recently been commercialised, their success has come at the expense of decreased performance due to design changes necessarily imposed to prevent device failure. However, more high performance switches could be developed if the mechanisms responsible for reliability problems could be understood and solved. The work of this thesis is focussed on the isolation and study of individual reliability mechanisms in RF MEMS capacitive switches. A bipolar hold-down technique is used to minimise the effects of dielectric charging and allow mechanical degradation to be studied in isolation in aluminium-based capacitive switches. An investigation of mechanical degradation leads to the identification of grain boundary sliding as the physical process responsible for the decreased mechanical performance of a switch. An alternative material for the switch movable electrode is investigated and shown to be mechanically robust. The effects of dielectric charging are isolated from mechanical degradation using mechanically robust switches. The isolated investigation of dielectric charging leads to the identification of two major charging mechanisms which take place at the bulk and surface of the dielectric, respectively. The exchange of charge from interface traps is identified as the physical mechanism responsible for bulk dielectric charging. An investigation of surface dielectric charging reveals how this reliability concern depends on the structure and design of a switch. Finally, electrical and material means of minimising dielectric charging are investigated. The findings and results presented in this thesis represent a significant contribution to the state-of the- art understanding of RF MEMS capacitive switch reliability. By implementing the design changes and material solutions proposed in this work, the performance and lifetime of RF MEMS capacitive switches can be greatly improved
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