Structural and electrical characteristics of SrTiO3 thin films for dynamic random access memory applications

Abstract

Polycrystalline SrTiO3 thin films having perovskite structure were prepared by the metallo-organic solution deposition technique on platinum coated silicon and bare silicon substrates. Crack free and crystalline films with uniform composition and thickness were fabricated by spinning and post deposition rapid thermal annealing at a low temperature of 550 °C for 60 s. The films exhibited good structural, dielectric, and insulating properties. The dielectric constant was found to depend on film thickness and annealing temperature. The small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 225 and 0.008, respectively, for a 0.8-μm-thick film annealed at 700 °C for 60 s. The frequency dependence of the dielectric constant and the dielectric loss was also studied. The measurement of the current-voltage (I-V) characteristics on films in metal-insulator-metal configuration indicated the conduction process to be bulk limited. The I-V characteristics were ohmic at low fields and space-charge limited at high fields. Room temperature resistivity of 1013 Ω cm and leakage current density of less than 10−8 A/cm2 were obtained for a 0.8-μm-thick film at an applied electric field of 200 kV/cm, establishing good insulating behavior. The interfacial properties of gold-strontium titanate-silicon structures were studied experimentally by measuring the capacitance-voltage (C-V) characteristics. The C-V curves exhibited anomalous frequency dispersion behavior and a hysteresis phenomenon. The hysteresis in the C-V curve was found to be about 0.8 V and of a charge injection type. The density of interface states recharged during the bias cycle in hysteresis measurement was estimated to be of the order of 8.3×1011 cm−2. The density of interface states at the flatband voltage was found to have a value of 1.38×1012 eV−1 cm−2. For a 0.5-μm-thick SrTiO3 film, a unit area capacitance of 3.5 fF/μm2 and a charge storage density of 36.7 fC/μm2 were obtained at an applied electric field of 200 kV/cm. These measured parameters place SrTiO3 as one of the suitable dielectric material for dynamic random access memory applications.

Electrothermal properties of perovskite ferroelectric films

“…This shift in T C arises due to the modification of the quadratic dielectric stiffness coefficient, depending on the magnitude of the thermal strain [Eqs. (32) and (38)]. As shown in Figure 16, the thermal strains produce a decrease in the zero-field value of T C of BTO, BST 60/40, and PTO on Si and c-sapphire when compared to their bulk values.…”

“…There is a significant interest in STO thin films as a replacement for the traditional gate oxide material SiO 2 [31], in dynamic random access memories (DRAMs) [32], and tunable microwave telecommunication devices due to their high dielectric response (~ 300 in STO single-crystals) and its strongly non-linear applied electric field dependence [33,34]. It is, therefore, crucial to understand the role of thermal stresses on the dielectric properties of STO thin films, especially for films synthesized using industry-standard deposition techniques (such as sputtering or metal-organic solution deposition) which usually produce polycrystalline STO films.…”

Band alignment at memristive metal-oxide interfaces investigated by hard x-ray photoemission spectroscopy

“…However, we note that a variety of charge transport mechanisms have been discussed for electrically treated SrTiO 3 , including resonant tunneling [35], polaronic conduction [36,37], and space-charge limited conduction (SCLC) [38]. All of the above (and others) exhibit nonlinear charge transport as a function voltage.…”

Μελέτη Και Βελτιστοποίηση Των Ηλεκτρικών Ιδιοτήτων Λεπτών Μονωτικών Υμενίων Που Χρησιμοποιούνται Σε Μικρο-Ηλεκτρο-Μηχανικά Συστήματα (MEMS)

“…Σε ένα διηλεκτρικό χωρίς παγίδες, όταν η εφαρμοζόμενη διαφορά δυναμικού είναι μικρότερη από: (2.28) οι φορείς που εισέρχονται στο διηλεκτρικό είναι λιγότεροι από τους αντίστοιχους φορείς που υπάρχουν σε κατάσταση θερμικής ισορροπίας και η σχέση πυκνότητας ρεύματος -τάσης (J-V) είναι ωμική [57], [58]: (2.29) όπου J είναι η πυκνότητα ρεύματος, V είναι η εφαρμοζόμενη διαφορά δυναμικού, q είναι το στοιχειώδες ηλεκτρικό φορτίο, n0 είναι η πυκνότητα των φορέων, μ είναι η ευκινησία τους, ε0 είναι η διηλεκτρική σταθερά του κενού, εr είναι η σχετική διηλεκτρική σταθερά του υλικού και d είναι το πάχος του διηλεκτρικού υμενίου. Για υψηλότερες τιμές της διαφοράς δυναμικού η σχέση J-V έχει βρεθεί [57], [58] ότι υπακούει τον νόμο του Child: (2.30) όπου η σταθερά Θ αναφέρεται στο λόγο της πυκνότητας των ελεύθερων ηλεκτρονίων προς την πυκνότητα των παγιδευμένων ηλεκτρονίων (για διηλεκτρικό χωρίς παγίδες ισχύει Θ = 1).…”

“…Για υψηλότερες τιμές της διαφοράς δυναμικού η σχέση J-V έχει βρεθεί [57], [58] ότι υπακούει τον νόμο του Child: (2.30) όπου η σταθερά Θ αναφέρεται στο λόγο της πυκνότητας των ελεύθερων ηλεκτρονίων προς την πυκνότητα των παγιδευμένων ηλεκτρονίων (για διηλεκτρικό χωρίς παγίδες ισχύει Θ = 1).…”