Chapter 3 Experiment
3.3 Measurement Process
3.3.1 Introduction
The data measurement is by the HP4156 semiconductor analyzer, the resolution is higher than 3pA. The measure included checks the device work. The measurements are device check, output characteristics and switching time measurement.
3.3.2 Device check
In our structure, we have two diodes, one is Emitter-Base diode the other is the Base collector. The Emitter-Base diode needs to inject the carrier. So we more care about its forward current. But the hold diode character still very important, it can help us to make sure the interface problem. For the Base-Collector diode, we need to reduce the reverse current which is the leakage of the device. This figure is the diode in the transistor, in the range of voltage operation; we can get very good diode characteristics.
Emitter-Base diode
For this diode, due to the device is operation under the forward bias when we check this diode will mention about the diode forward current. But the reverse current still need to check because it can show out the interface problems.
Figure 3-12 Emitter-Base diode measurement
Base-Collector diode
The Base-Collector diode is a very important part of our device which can decide the device output characteristics. In our structure, the Base-Collector is operated at the reverse bias. And the reverse current is the leakage of the device because the output current does not come from the reverse current is come from the hot carrier ballistic transport. The reverse current of device must be as low as possible.
Figure 3-13 Base-Collector Diode Emitter Collector leakage
Although the leakage is decided by the Base-Collector diode reverse current, there still have another possible leakage from the structure or the process error. So we apply the operation voltage to test the leakage when the device operation.
Figure 3-14 Emitter-Collector Leakage measurement
3.3.3 Output Characteristics
Common Emitter mode
This mode is the condition of device operation. Due to the carrier of the device is hole. In this mode, the emitter is grounded. Base offer a static negative current. Under normal bias the emitter-base diode operate in the forward bias. Then scan collector voltage from 0 volt to -5 volts.
Figure 3-15 Common Emitter Mode measurement
Common Base mode
In this mode base grounded. The emitter injects a static current. Final, scan collector voltage and measure the collector.
Figure 3-16 Common Base Mode measurement setup
Chapter 4 Data Analysis
Common Emitter Mode:
The common emitter output characteristic is shown in the figure 4-6. First, we calculate the current gain when the voltage is -5 volts the current gain average is . But it is clear that the current gain is not a fix value, that is because the image force lowering. We can fine this when plot the relation of base voltage various with the collector voltage. In our structure, there is a LiF layer which helps the carrier injection and increase the energy different between the emitter and collector. There is another problem which is the leakage of this pixel about few micron amperes. The order of leakage does not the theory expected leakage order. The leakage should be comes from the structure leakage.
53
Figure 4-1 Common Emitter Mode Data of 2004.10.14
Common Base Mode
In this mode, we can observe the transport behavior. And the transport factor 0011
α = . In this mode, emitter injection current into the collector
-3 -2 -1 0 1 2 3 4 5 6
Figure 4-2 Common Base Mode Data of 2004.10.14
Emitter-Base diode
We check the forward current because this part determined the injection current order and the diode behavior will help us to determine the interface condiction.
-5 -4 -3 -2 -1 0 1 2 3 4 5
Base-Collector Diode
The Base-Collector diode we will mention about the reverse current because this part will decided the device leakage order. The leakage order should be less than the order of Base-Collector diode reverse current order.
-5 -4 -3 -2 -1 0 1 2 3 4 5
This will decided the leakage current when the device operation. This device leakage maximum about 2nA and the average leakage current less than 0.5 nA.
-6 -4 -2 0 2 4 6
Chapter 5 Conclusion
Our result demonstrated the first polymer hot carrier transistor on the glass substrate. Moreover, the current went up to 29.33. Also, this device has nice output characteristics. The most important thing is that the transportation factor closes to 1.
That means if there is enough carrier injection, the current gain can be achieved to the commercial level. However, the process of increasing carrier injection is not easy to control. In the future, there are two main issues of hot hole transistor to be solved. The first one is to increase the injection current and the second one is to reduce the device leakage.
Reference
[1] STEPHEN R. FORREST,” The path to ubiquitous and low-cost organic electronic appliances on plastic” Nature 428,pp. 911 - 918 ,29 April 2004.
[2] L. P. Ma, J. Liu, Y. Yang,”Organic electrical bistable devices and rewritable memory cells” ,Applied Physics Letters ,Volume 80, Issue 16, pp. 2997-2999, April 2002.
[3] Natalie Stutzmann, Richard H. Friend, Henning Sirringhaus,”Self-Aligned, Vertical-Channel, Polymer Field-Effect Transistors”, Science, Vol 299, Issue 5614, 1881-1884 , March 2003.
[4] R. Parashkov, E. Becker, S. Hartmann, G. Ginev, D. Schneider, H. Krautwald, T.
Dobbertin, D. Metzdorf, F. Brunetti, C. Schildknecht, A. Kammoun, M. Brandes, T. Riedl, H.-H. Johannes,W. Kowalsky, “Vertical channel all-organic thin-film transistors”, Applied Physics Letters ,Volume 82, Issue 25, pp. 4579-4580 ,June 2003.
[5] M. S. Meruvia , I. A. Hümmelgen ,M. L. Sartorelli ,A. A. Pasa, W. Schwarzacher,
“Organic-metal-semiconductor transistor with high gain” Applied Physics Letters ,Volume 84, Issue 20, pp. 3978-3980, May , 2004.
[6] J. C. Hensel, A. F. J. Levi, R. T. Tung, and J. M. Gibson ,”Transistor action in Si/CoSi2/Si heterostructures”, Applied Physics Letters ,Volume 47, Issue 2, pp.
151-153 July 1985.
[7] N. Evers, J. Laskar, N. M. Jokerst ,T. S. Moise, Y.-C. Kao ,”Direct current and high frequency performance of thin film InP-based tunneling hot electron transfer amplifiers”, Applied Physics Letters ,Volume 70, Issue 18, pp. 2452-2454 ,May 1997.
[8] T. S. Moise, Y.-C Kao, A. C. Seabaugh ,”Room-temperature operation of a
tunneling hot-electron transfer amplifier”, Applied Physics Letters, Volume 64, Issue 9, pp. 1138-1140 February 1994.
[9] Z. Chiguvare, J. Parisi, V. Dyakonov,”Current limiting mechanisms in indium-tin-oxide/poly3-hexylthiophene/aluminum thin film devices”, Journal of Applied Physics ,Volume 94, Issue 4, pp. 2440-2448 ,August 2003.
[10] S. C. Jain, W. Geens, A. Mehra, V. Kumar, T. Aernouts, J. Poortmans, R.
Mertens,M. Willander ,”Injection- and space charge limited-currents in doped conducting organic materials”, Journal of Applied Physics, Volume 89, Issue 7, pp. 3804-3810 ,April 2001.
[11] V. R. Nikitenko, H. Heil, H. von Seggern .”Space-charge limited current in regioregular poly-3-hexyl-thiophene” Journal of Applied Physics, Volume 94, Issue 4, pp. 2480-2485, August 2003.
[12] David R. Penn,” Electron mean-free-path calculations using a model dielectric functions”, Phys. Rev. B 35, pp.482–486, January 1987
[13] N. G. Ptitsina, G. M. Chulkova, K. S. Il’in, A. V. Sergeev, F. S. Pochinkov, E. M.
Gershenzon. M. E. Gershenson ,”Electron-phonon interaction in disordered metal films: The resistivity and electron dephasing rate”, Phys. Rev. B 56, pp.10089–10096 , October 1997.
[14] I. Campillo , V. M. Silkin , J. M. Pitarke , E. V. Chulkov , A. Rubio, P. M.
Echenique,” First-principles calculations of hot-electron lifetimes in metals”,Phys. Rev. B 61, pp.13484–13492 ,May 2000.
Appendix A:
The Measurement Items that we need to Measure Because there are lots of problems we have during develop the Polymer Hot Hole Transistor, there are some measurement note that we need to measure to make sure the process and the parameters is correct. I list as follow:A.1 ITO paten check:
After we defined the paten on the ITO, need to measure the leakage between the cathodes.
A.2 the Base resistances check
After we evaporate the thin base layer we need to measure the sheet resistances to make sure the thickness is correct. This process need to measure in the glove box because the Al wills oxidation easily.
A.3 Diode check
This is the basic device characteristic to make sure the device can work or not.
Do not apply high voltage that will make the device broken.
A.4 Leakage check
Make sure the leakage order when device operation.
A.5 Common Emitter Mode
This is the device operation mode. After apply the base current form low to high, for example: from 0nA to 100nA, apply the base current in the reverse sequence that means from high to low, for example from 100nA to 0nA. The purpose to reverse the
sequence is to make sure the device does not have memory effect.
A.6 Common Base Mode
This mode is to determinate the current injection behavior. The same as the A.5, need to reverse the Emitter current apply sequence.
A.7 Switching Time
Do not mix with the response time. This is to determinate the switching time when it operation.
Appendix B:
The trouble shooting of process of hot hole transistor During this experiment we mete lots of mistakes. These mistakes will not help researcher to improve device performance. But will help the researcher to find the problems rapidly and how to solve to reduce the cost and time of researching process.1. Step Covering
In the Polymer Hot Hole Transistor, the process has a big point need to mention about is the step covering. Due to the polymer layers thickness are micro meter orders. So those, the contact are some time will broken. There are some situation and the perhaps reason come from the step covering problems.
(1) The Emitter diode only have few nano ampere current output and the the Base diode the same with Emitter characteristics. In this situation, if to measure the common emitter characteristics in the high voltage region there will be have the characteristics as the follower. In this situation, the current gain close to infinity because we need almost zero base current but this is due to the memory effect.
Figure B-1 The memory effect
ÆShould be the base too thin or contact Al do not cover partially P3HT layer region
(2) Only Base diode is work and Emitter only have few nano ampere current output.
ÆShould be the Au layer too thin, make sure the thickness more than 50nm.
(3) Both Base diode and Emitter diode can work but the Emitter-Collector have high leakage current (much higher than the Base diode reverse current)
ÆShould be the ITO paten does not etching well so that there are some parts are short. This can be solve by checking the ITO paten leakage.
2. Evaporate
In the metal base transistor, the more difficult part is to control the base layer. And for our structure, the Au evaporate conditions will decided the injection current order. So these two parts’ parameters must be control very careful and exactly.
(1) Base evaporates:
Due to us need very thin Al layer, the cleaning and vacuum level need keep very well. The evaporate rate as low as possible. Then we need to change the evaporate the shadow mask to evaporate the contact Al, make sure all the processes are in the glove box before we evaporate the contact Al layer.
(2) Au evaporates:
Because of the emitter current injection need to overcome a high barrier, we evaporate the Au film in very high evaporate rate to make tips in the PVK layer to produce localize high voltage. But the condition is difficult to control, we need to make more sample to make sure to get the sample. In the other words we have low yield. The better way to enhance the yield is to control the evaporate parameters carefully. The better condition we found are evaporating in the high evaporates rate and short time. The short evaporate time better because the heat produce by the boat will enhance the Au moving deeply make the device short.
3. Powder problems:
Although the polymers powder what we use is commercial goods. Most polymers brought from Aldich. But there still have some different between two polymers that brought at different. For example: there are polymer 1 and polymer 2. The two polymers are the same type but the molecular weights have few different. The recipe of polymer 1 may not suit for polymer 2 because of the difference of molecular weights. There are some thing need to check to avoid this condition:
(1) Check the data sheet carefully.
(2) Making a standard sample.
(3) Retry the parameters of the new powder.