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arsenal_he

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ultrasim vs spectre
Apr 09^th, 2007, 6:09pm

hi,

i am runing some simple simulation using ultrasim and spectre.
For a transistor with fixed biases, spectre shows id=260uA while ultrasim only gives out 50uA with the same model and corner and highest accuracy setting.
And the spice model shows that spectre simulation gives the correct results, then what can i do such that ultrasim runs fine？

thanks
arsenal

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sheldon Community Fellow Offline Posts: 751	Re: ultrasim vs spectre Reply #1 - Apr 10^th, 2007, 6:05am Arsenal, You need to provide more information about your circuit and any warnings in the log file. In particular, was the dc operating point calculation correct? Best Regards, Art Schaldenbrand
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arsenal_he

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Re: ultrasim vs spectre
Reply #2 - Apr 10^th, 2007, 11:19am

hi art,

thank you for your reply.
I didn't find any warnings but the vth of ultrasim simulation is 0.658v while that of spectre is only 0.420v.
Then why is so big difference of vth?

thanks
arsenal
sheldon wrote on Apr 10^th, 2007, 6:05am:

Arsenal,

You need to provide more information about your circuit and any
warnings in the log file. In particular, was the dc operating point
calculation correct?

Best Regards,

Art Schaldenbrand

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Geoffrey_Coram Senior Fellow Offline Posts: 1999 Massachusetts, USA	Re: ultrasim vs spectre Reply #3 - Apr 10^th, 2007, 12:11pm Do your models include WPE or STI stress effects (parameters SA, SB, SC)?
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arsenal_he

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Re: ultrasim vs spectre
Reply #4 - Apr 10^th, 2007, 1:31pm

hi Geoffre,

I found some warnings complaining lack of sa1 so ultrasim use sa instead. BUt I did'nt find any sa1 or sa in the model file. And I have checked both the netlist of ultrasim and spectre, both of them have the parameters of SCA, SCB, SCC

thanks
arsenal
Geoffrey_Coram wrote on Apr 10^th, 2007, 12:11pm:

Do your models include WPE or STI stress effects (parameters SA, SB, SC)?

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« Last Edit: Apr 10^th, 2007, 5:42pm by arsenal_he »

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Geoffrey_Coram

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Re: ultrasim vs spectre
Reply #5 - Apr 12^th, 2007, 4:39am

SA/SA1 are instance parameters, meaning that the instance should have values that indicate how that particular device is laid out; AD, AS, PD, PS are also instance parameters. The model file describes common parameters. If ultrasim is using the wrong values for the stress parameters, then it will incorrectly compute the shift in threshold voltage due to stress.

If it's a small test netlist, you could delete all the sa/sb/sc parameters and see if you get the same threshold voltage. Then we can work on seeing if we can fix the parameter names. Eg, "sa1" is not an official BSIM parameter, it is part of a foundry-specific STI stress model; there are values SA1 through SA9 for up to 9 gate segments. It may be that ultrasim doesn't support these unofficial parameters.

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If at first you do succeed, STOP, raise your standards, and stop wasting your time.

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arsenal_he

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Re: ultrasim vs spectre
Reply #6 - Apr 12^th, 2007, 11:35am

hi Geoffrey,

thank you very much.
I found that it was due to the calculation of SCA,SCB and SCC, which should change as to W/L, but my those parameters in my pdk are fixed! Still i don't know where to get a new pdk for tsmc65gp

thanks
arsenal
Geoffrey_Coram wrote on Apr 12^th, 2007, 4:39am:

SA/SA1 are instance parameters, meaning that the instance should have values that indicate how that particular device is laid out; AD, AS, PD, PS are also instance parameters. The model file describes common parameters. If ultrasim is using the wrong values for the stress parameters, then it will incorrectly compute the shift in threshold voltage due to stress.

If it's a small test netlist, you could delete all the sa/sb/sc parameters and see if you get the same threshold voltage. Then we can work on seeing if we can fix the parameter names. Eg, "sa1" is not an official BSIM parameter, it is part of a foundry-specific STI stress model; there are values SA1 through SA9 for up to 9 gate segments. It may be that ultrasim doesn't support these unofficial parameters.

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« Last Edit: Apr 12^th, 2007, 3:18pm by arsenal_he »

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Geoffrey_Coram Senior Fellow Offline Posts: 1999 Massachusetts, USA	Re: ultrasim vs spectre Reply #7 - Apr 13^th, 2007, 6:45am You may need to get a layout-extractor that supports WPE (SCA,SCB,SCC).
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arsenal_he

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Re: ultrasim vs spectre
Reply #8 - Apr 13^th, 2007, 3:35pm

ya, im using qrc to do the RCX, and it seems SCA,SCB and SCC affect vth too much! i did an experiment and the pre-layout vth is about 470mv while the post-layout is 690mv!!! How can i minimize the discrepancy in layout?

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Geoffrey_Coram wrote on Apr 13^th, 2007, 6:45am:

You may need to get a layout-extractor that supports WPE (SCA,SCB,SCC).

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sheldon Community Fellow Offline Posts: 751	Re: ultrasim vs spectre Reply #9 - Apr 13^th, 2007, 10:22pm Arsenal, Can you modify the transistor layouts? These parameters are a function of layout. BTW, did a quick search and found an interesting paper that might give you insight into what needs to be changed, http://www.ieee-cicc.org/06-8-6.pdf Best Regards, Sheldon
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arsenal_he

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Re: ultrasim vs spectre
Reply #10 - Apr 17^th, 2007, 3:47pm

Sheldon,
Thank you very much.

arsenal
sheldon wrote on Apr 13^th, 2007, 10:22pm:

Arsenal,

Can you modify the transistor layouts? These parameters are a
function of layout. BTW, did a quick search and found an interesting
paper that might give you insight into what needs to be changed,

http://www.ieee-cicc.org/06-8-6.pdf

Best Regards,

Sheldon

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