Alison J Tessmer

Diamond devices and electrical properties

Abstract Diamond offers tremendous potential for electronic applications such as field effect transistors. An investigation of the electrical properties of boron-doped homoepitaxial diamond films and the metal-oxide-diamond gate structure was performed. Additionally, field effect transistors were fabricated and characterized. Improvements in the diamond deposition process produced boron-doped homoepitaxial diamond films where the room temperature Hall mobility exceeded 1000 cm 2 V −1 s −1 . Analysis of the temperature-dependent carrier concentration indicated that the compensation was 15 cm −3 . The gate structure for metal-silicon dioxide-boron-doped diamond field effect transistors was evaluated by current-voltage and capacitance voltage measurements. Good correlation of the uncompensated acceptor concentration, determined by capacitance-voltage measurements, and the boron concentration, determined by secondary ion mass spectroscopy, was attained. Preliminary measurements suggested that the density of interface states for this structure was ≈ 10 12 cm −2 eV −1 . Field effect transistors exhibited saturation and pinch-off at temperatures as high as 773 K. The highest normalized transconductance measured was 1.3 mS mm −1 . The field effect transistors were combined into analogue and digital circuits that operated at 523 K and 673 K, respectively.

Polycrystalline diamond field-effect transistors

Abstract The first demonstration of field-effect transistors fabricated from polycrystalline diamond thin films is reported. Diamond thin films were deposited by a microwave plasma chemical vapor deposition technique. The surface roughness was removed by polishing using a SiO x chemical machining technique. Ion implantation was employed to form a B-doped conducting surface channel with an approximate carrier concentration of5 × 10 18 cm −3 . A low temperature deposition of SiO 2 was used to form the gate dielectric structure. Gate leakage currents were below 10 nA at 25 V. Although the channel did not reach the pinch-off condition, modulation of the channel conductance was observed.

High-temperature operation of polycrystalline diamond field-effect transistors

Operation of polycrystalline diamond field-effect transistors (FETs) at temperatures up to 285 degrees C and drain-to-source voltages of up to 100 V has been demonstrated. The devices were fabricated from B-doped polycrystalline diamond grown by a microwave plasma-enhanced chemical vapor deposition (CVD) technique. At 150 degrees C, the devices exhibited saturation of drain current and a peak transconductance of 65 nS/mm. These are the first polycrystalline diamond devices to demonstrate saturation. Device characteristics at 250 degrees C also show saturation and increased transconductance of 300 nS/mm. Characterization was not performed at temperatures exceeding 285 degrees C due to gate leakage current above 10 nA.<<ETX>>

Diamond Field-Effect Transistors

Metal-oxide-semiconductor field-effect transistors (FETs) have been fabricated using B-doped diamond thin films deposited on polycrystalline, (100) highly-oriented, and single crystal diamond insulating substrates. Diamond films were grown using a microwave plasma chemical vapor deposition technique. Various electrical and materials characterization techniques were employed to confirm that the films exhibited properties suitable for FET fabrication. Devices with gate lengths and widths of 2 μm and 314 μm respectively, were processed using standard photolithography. Silicon dioxide was used as the gate dielectric. Current-voltage characteristics of these devices have been measured during variable temperature cycling in air. Devices fabricated on the randomly oriented polycrystalline diamond substrates have been operated to 285°C. Field-effect transistors fabricated using the highly-oriented diamond substrates have been characterized to 400°C. Single crystal diamond devices exhibited saturation and pinch-off of the channel current at temperatures up to 500°C. These devices have been biased in amplifier circuit configurations that have been characterized from 20 Hz to 1 MHz. Single crystal FETs exhibited voltage gain over an extended temperature range. Transconductances as large as 1.7 mS/mm have been observed. The electronic properties, fabrication technologies, and performance of devices fabricated on the three diamond substrate materials will be discussed and compared.

Current-voltage characteristics of in situ doped polycrystalline diamond field-effect transistors

Summary form only given. The authors report the first demonstration of a polycrystalline diamond (PCD) FET which exhibits saturation and pinchoff. The PCD material was grown by a microwave enhanced chemical vapor deposition technique. Following room-temperature characterization, the devices were tested at elevated temperatures in atmosphere. As the temperature was increased, the current level increased significantly. At a temperature of 150 degrees C, the zero gate-bias drain-to-source current was -34 nA at -20 V and the channel resistance had dropped to 990 M Omega . The drain to source I-V characteristics were linear at this temperature. Gate voltages were applied in 8-V steps while the drain-to-source voltage was swept from 0 to -30 V. The I-V characteristics clearly showed evidence of saturation. Also, at applied gate biases in excess of 32 V, the active channel is pinched off. The peak transconductance at 150 degrees C was 6.4 nS/mm. Device failure occurred at a temperature above 200 degrees C and was due to failure of the gate oxide layer. >